I would recommend puttin in the 350. I had the same choice and decided to just rebuild the 305 because I didn't know if anything else on the car worked the way it was supposed to :/ It ended up costing me about as much as a new 350 truck motor would have been brand new. You can also find people selling these motors all over the place, being the most popular sb. I found a 350 block with rotating assembly for $50 now mind you it's only a 2 bolt main, but for what you will be doin will be great. Hell, I would give you the block and rotating assembly for $50 disassembled because I want a 4-bolt for a 383 stroker, but I doubt you're in texas. Anywho, the 350 is the way to go

 

i would go for the 350 4-bolt, the guy i got my camaro from swapped out the 305 for this and said it was reletivly cheap if you get a rebuilt one and just use the 305 parts (ie altenator, starter, water pump ect)