Heres what I do.

Fit the disc stop to the outer cable :- Clamp outer in a vice with approx 1/2 inch protruding, drop disc over it, use a pair of side cutters to unwind a turn and a half, hammer this coil flat against disc and cut off excess leaving one complete turn flattened against disc, this won't pull out. 

Feed inner thru hole in bars near headstock, and use this as a guide for the outer. Have a friend pull on outer stretching it slightly while you fit small clips up tight against handlebar, this will remove all slop from outer.

pin  should be a light press fit into barrell, some may need a slight adjustment, they normally have a slight taper so one end will feed in easier. put a 90 degree bend in inner with a tail just under half length of pin, for clean bend use vice and small hammer.Feed that tail thru small hole and push pin thru, sandwiching tail in the groove. May need pressure in vice and socket on one end to force thru. make sure it is even both sides. You may have burred up the barrell doing this, file to clean up, as these will affect action. 

There may be burrs on the inside of handlebar slots, remove these with fine file taking care not to open op slot, burrs will cause snatchy action, wide slot will cause slop.

Now feed inner down outer using white grease liberally. Fit twistgrip with internal spiral over bar and wind it on. Now tighten up ring and check for play. some new grips may jam as the return on the end of the twistgrip is too thick, I have had to turn down up to 60 thou off them to stop them jamming. Some may be too thin, this will cause slop, Greers sell a shim kit.if you have a smooth action now, disssemble, fill up liberally with white grease and put back together. 

Before fitting rubber  handgrips, check depth, usually tight fit and often 1/4 inch to short, leaving unsightly gap between rubber and bar. Increasing depth a touch is not difficult, there is up to an inch of solid runner there. Find an appropriately sized endmill but in lathe chuck and trun at low speed,pushing grip on, CARE NEEDED HERE> .You will need to drill a small hole in the centre of the solid grip end only as deep as you need to remove rubber, to allow mill to cut, as the centre of the mill bit which does not cut will stop contct with the rest of the rubber.

Don't cut cable to length until you are sure routings and free play are correct, leave tails of inner as long as possible at the carb or mag end, often people cut them short and put a 90 bend in them just past ferrule, then find they need adjustment. They cables shuld be adjusted so that full advance on mag or trhottle fully closed on carb is just before full movement of handgrip, a little extra legth will add pressure to carb closing or full advance being achieved. Some fiddling may be requires to get full movement of throttle disc, push disc shut with screwdriver before adjusting cable. Fully closed obviously more important than fully open :)

The leather bale prtectors are great, without them the cable will remove all paint from headstock in a couple of hundred miles. 

Let me know how you go, or if anything needs clarifying, its pre morning coffee here.

Tim

Yes, that's a good guide. In addition I can say when bending the inner wire 90 degrees for the slider block, I had to pre-bend the wire as much as possible, then insert it in the slider block and let the pin shape the last when knocking it in. I could enter the pins in the holes but they needed persuing with light hammer blows. I had to avoid the block make a nick on the wire at the inner curve, so I went in there first with a dremel ballshaped grinding bit, to countersink the hole just a touch. At pre-bending I did use a aluminium coaster for the vice. The bend has to be tight but still as round and smooth as possible. All that to prevent any unneeded strain and fatigue break at that critical point.

The outer sheeth is very VERY sensitive for any damage, slightest blow on it, kink or tight bend makes the wire tight. Much more sensitive than a bowden wire, because the gap between the wire and hole is much smaller. The bend around the headstock is most critical, just a tad too short and you got a tight bend on it when you turn the handlebar to the ends. Just a tad too long and you got a kink where it enters the handlebar or/and a kink at the bracket!

Don't force the wire anyplace, take the care and time it takes to adjust the length exact and the controls are rewarding you with wonderful smooth and precise movement.

A kink or bend is hard but not impossible to fix, but it takes a lot of meticulous careful bending with dual pliers. Most times it is better to pull out the wire first, you still need to straighten the inner wire in any case. Fix the outer sheeth first so you can compare where the kink is with the damage on the inner wire. It is good if you have experience on how to manipulate a tight wound spring. Avoid tapping, a flat spot and you have to scrap the sheeth altogether. If you fix the inner wire first, you will have a very hard time to find the damage on the outer sheeth.

Ps. My twistgrip tubes is about 3/4" shorter than the rubber grips. That leaves a air cushion and soft handlebar end, that has shown very useful when manouvering in tight places! No damage to grips, walls or other vehicles when accidently bumping in to them! I love it.

With the inner fed thru first as a guide, finding a way to rotate the outer usually gets it to pop thro. Again , taking care not to kink the outer, I loop up the other end in a large coil so that I can spin it easily. Sometimes you may need to wiggle the "guide" inner too at the same time, requires 3 hands :)

I found a video that Mike Thomas of KIWI has made and it gives some valuable tips that can be applied to the 101 cable and grips installation. 

https://www.youtube.com/watch?v=o5iynnkzay0

Sorry to hear about your troubles. Was the pin ruined when pushed out again? If not, just a little sanding would fix the tight fitting. And if it was, if you find a pin that fits the hole it shouldn't be that difficult to produce the groove and notches with a Dremel and a little fiddling.