The knob on the side of the distributor is actually for lubrication of the distributor shaft bushing. It would be filled with grease, then the knob is turned 1 turn every 1000 miles to force grease into the bushing. Unfortunatly, many times this was not done, and the bushing runs dry, leading to prematrue shaft wear.
To answer the second qustion, if you're looking for a true HEI, you would be changing out the entre distributor, there isn't a way to convert. Langdons has HEI distributors that are already modified to work in the 235. If you mean to eliminate the points, Pertronix makes a kit that will work in your existing distributor.
