It does sound like a vacuum leak although I was having similar trouble with my rebuilt 235. I was using a different flywheel and checked TDC was not the same as before. I needed to advance significantly. I set the engine at TDC (by looking in the #1 sparkplug hole)and marked the flywheel
You can spray some wd 40 on the intake manifold conections and carb base to see if the engine changes idle temporarily that could help you narrow down the leak.
You can also set the timing by vacuum. Advance the dizzy until max vacuum is achieved. You can do the same with the carb idle adjustment. A vacuum gauge is a very versatile tool.
