Finally got assistance, tools, advice and the nerve to attack penetrating the rear plug, in this project to convert from Constant Speed to Fixed Pitch on my O320.
Also this SB:
http://www.lycoming.com/Portals/0/te...rsa;%20....pdf
The rear plug is approx. 7 inches deep into the crank, from the forward edge of the crank.
I used a long 1/8th drill bit and a very slow drill technique. Repeatedly coated and cleaned off a heavy dab of grease, capturing tiny particles (fine like grains of sand). Great help from Mark, whose building his own RV7.
After drilling the hole another plug installed on the crank's end, engine run, and NO LEAKS! It's a good day!
Carl