Noone else seems to be here on the forum.... Hello!!

I vote stay out! All old castings are oil saturated and even if you boil it out, there's a risk of the paint to flake.

If you choose to do it anyway, and the factory did it in some later engines, just use very thinned paint and dry it in an oven. The purpose is only to have the pigments to fill a porous casting to avoid leakage... but do you have a pore in the casting? Paint was used in racing motors to help oil run back to the sump, but that is for engines on circle tracks and the effect is so marginal and not a factor in the Indian engine for several reasons.