88MCsupersport said:
a 5.7 ls is a 350 with fuel injection, you'll also need to change your engine wiring harness if you put a carbureted 350 you can keep the same harness and it'll be cheaper and faster to do the swap personally its all what you prefer, shop around and see what go fast parts you can get for both engines see which ones are cheaper and that you would prefer to install.
Not to be rude but a 5.7 ls is not simply a 350 with fuel injection, not even close. maybe a vortec 350 you could make a case for that but thats about it. Ls1 is actually 346 ci and theres not a single sbc part that will fit on the engine. completley different animal but much more responsive to mods imo. Theres a lot more info on them and a huge following which means a huge aftermarket of performance. If wiring is a big deal consider the fact that you can get truck style (lq4) computers for around $50-$100 and and there are tons of stand alone wire companies out there if thats a major concern to anybody. PSI is one of the cheaper quality companies and there harness run around $500.
To the OP...
a 350 sbc is is pretty simple direct swap, but your not going to get a lot of performance out of it without putting money into the motor. The LS is a much better starting point and will respond much better with cheaper mods that have just a big of an aftermarket as any sbc motor would. For me I would do a LS without hesitation. Theres lots of builds threads out there on swapping LS's into g bodys and if your serious about it I would check out LS1tech.com to really get an idea of the power levels, costs, and work that has to be done to put a LS in one. I would also look at LQ4's rather than LS1's ( its the iron-block Ls2 engine basically that were used in 3/4 and 1 ton trucks and is much much cheaper than a alum ls1 block). In the end its up to the amount of work you want to do and money you want to spend. For me id rather do something one time and be done with it and be happy with it. If you think a carbed 350 will do that for you then go for it.