Most folks here will recommend the Carter. I have run Carter's on other engines and they all worked very good so if you're gonna replace the carb look at a Carter. Carter made many different models, you can do a search for "carbking" and Carter as he put together a very detailed Carter application list. He may be along.
re. the Roch B. Sounds like the power piston isn't working properly or probably not working at all. It works off of vacuum to allow more fuel into the venturi when the engine is under load. If it sticks "open" it'll allow too much fuel at all times, i.e. poor MPG.
If it sticks "closed" it'll never allow more fuel when needed, i.e. low power.
Make sure the carb to manifold gasket has a hole in it to line with the vacuum ports at the bottm of the carb and in the insulator between the carb and manifold. This is where the power pistons control vacuum comes form.
I run a Roch B on a 49 216 and it performs pretty good. The 3100 avg's nearly 13 mpg and it'll pull hills in high gear and accelerate upto 65 to pass (I don't keep it there long tho).
My 49 was a one owner and was pretty much stock so that many contribute to the Roch B working as good as it does.
Good luck
