The problem could be 2 fold:
The BB on a 54 235 is 2 degrees ATDC. If your engine is stock I'd recommend to try resetting the timing to either the BB or at the UC (TDC) mark.
2 - 4 degrees doesn't sound like much but it is on an engine designed to idle at 2 degrees ATDC...
I had a similar problem with a modified 54 235 engine and I too tried to use the highest vacuum setting for the timing and it ended up being way too advanced. The engine would start and accelerate fine but would hit and miss at any steady rpm.
Try retarding your timing 1st.
2nd problem could be the power valve in the Roch B carb is sticking, that is what may be causing your over rich condition. It should move up/down easily in the carb. Make sure the check ball is installed under the spring on the power valve too.
Another possibilty is the gasket under the carb doesn't have the vacuum hole in it to allow vacuum to the power valve. On the bottom of the carb on the mounting flange you'll see a vacuum hole, this is for the power valve. At idle and slow speed driving the high vacuum signal keeps the power valve closed since additional fuel is not needed. If theres no vacuum the power valve will remain open causing excess fuel to feed into the venturi. The hole must be open through the gasket to the spacer which is cut/molded to allow vacuum to the carb.
Good luck
Dave
