Gawd help me, but I can't resist!
My first temptation is to say "put a Predator on it" BWAHAHAHAHAHAHAHAHA!
Now, that being said...
I had a 77 Impala with a 305. I put Corvette heads and Distributor, along with a stock GM Four barrel manifold and quadrajet on it. Ran like a raped ape! I would skip all the trick high-dollar parts and stick to some well thought-out junkyard swaps. The 305 is as maligned as the 307 of earlier years, but is STILL A SMALL BLOCK CHEVY!
There are TONS of parts for it, and you can make it respectable looking, with decent power. Fact is, the 305 is probably a better choice than the 350 as the power is a bit more tractable.
My suggestion: keep it stock until you get the quirks of the conversion worked out and see how you like the car. If you need more speed, THEN go for the mods.
Otherwise, do the things that reduce the mill's weight: small atarter, aluminum flywheel, intake, steel-tube headers, etc. Anything you put on the 305 will fit the 350, so it's transferrable if you "go bigger" later on!
If you have a 305 with the TPI, KEEP IT! There are stand-alone harnesses (Arizona Speed And Marine comes to mind) that allow this swap EASILY! Fuel injection kicks Carburetion any day of the week.
Unless you have a Predator, then all fall by the wayside in awe of your performance. (Again, the drink prevents my restraint of smartass coments--forgive me!)