The timing for the 305 would be on the radiator support. The timing for the 350 may be different depending on the camshaft, etc. Start with what is spec'd for the 305 and adjust +/- a couple degrees from there to where it runs best. Problems like the one you describe are seldom caused by timing though.
The choice is yours -
1. keep it legal and hook all the computer stuff again.
2. Install a non-computer, emmissions carb (Holley makes a 600 I believe) and a non-computerized distributor (out of an early HEI car say 1975 - 1981). A non-emmissions carb will probably run rich and eventually make your catalytic converter go bad.
[This message has been edited by Eric68 (edited 05-07-2001).]