Nick moss in UK made a bunch of these. Reach him at Nick_Moss@ripmax.com It mounts instead of the plug screw at the bottom, that screw has a thin washer of pure lead to seal in its special concave seat. Be sure to use (weak or medium) locktite when mounting the screw again.
The plug delete the transfer hole into the cam chest and the oil drops that the pump delivers go out of the check hole instead. With enough oil in the crankcase, the engine can run for at least 10-15 minutes on the stand without replenish by the pump, so there is no hurry to get the oil pump setting right.
The oil tester plug sets the initial setting for the pump for the first start of the engine when everything is unknown. With modern piston rings, the factory recommended amount of drops per minute is a bit too much. Oil level in the crankcase should be regulary checked, and oil pump setting adjusted accordingly until you get familiar with your engine's oil consumption.
Filling the crankcase with oil for the first time is best done in through the camchest, at least an amount of it, via the hole that the oil pump puts oil through or crankcase ventilation hole for those that have that on the cover. That way the cams and bushings get plenty of initial lubrication.
