[Eddy K]

David, I had that same problem when I installed a new pickup in my MSD distributer. The wires were reversed on the pickup. Fortunately I have a friend who is very well versed on this subject and diagnosed it over the phone. I reversed it and the engine straightened right out.
If the distributor is phased wrong it will throw your timing for a loop and will have all the symptoms you speak of.
As or the best carb for the street, a vacuum secondary carburator is most always the best choice for drivability. Probably for your engine, a 780 would work pretty well. However. I would talk to Holley or Grant, someone like that who is way more knowledgeable on this subject than I am.
I did install the 50 cc pump on my car today and although it is better, the stumble is still there. I am going to keep going at it and see if I can get it to work.
I also have one of the 750 Street Dominators setting on my shelf that I would like to try. I am sure that will be a bear to get working correctly.