Stupid question: have you replaced the plug wires? Sometimes it's the little things... Foul wires cause your timing to go haywire no matter what dizzy you use, and sitting for a year doesn't make your wires better. Check them.
Any cracked vac hoses? These can also cause your engine to run like the Dutch National football team...
Second:
Take off the carb and clean it (dissassemble and soak it in carb cleaner). recheck whether it runs better or not. Alternatively borrow a similar carb off a running vehicle (from a friend or steal it from somebody you don't like )
If that doesn't help it's not the carb, so buy a crate of beer and visit your friend again. Borrow his dizzy (if it's a HEI or a good running points type thing).
Mostly there's no need to dish out a chunk of greenies until you've found the problem.
I mostly look for the problem with borrowed parts (of which I know they work well) first before I start dismantling things for fun when I don't even know they're the cause of the problem...
If the car was in a really damp environment it's just possible that you have rust inside your engine, which will give you crappy running any time. Small burrs on the cylinder walls from long use won't catch oil and thus rust if exposed to dampness for a long time. This would mean a complete teardown... But that I guess is the worst case scenario...
I would check carb and ignition with borrowed stuff and come back here if it's none of this.
If you're not into racing this vehicle, don't go bigger than 650 cfm with the carb, i would even go for a 600 and a good manifold.
Hope I could help,
Max