Re: Swapping 305 and 350... Any tips?
The passengers manifolds are different. The 305 uses the 7th bolt hole, and the exhaust exits in front of the last exhaust port. The 350 manifolds use the 6th bolt hole, and exits behind the last exhaust port. Thus, making the "Y" pipes different. If you had converted to Headders, or dual exhaust using manifolds, you won't have a problem. If you change the "Y" pipes with them, you shouldn't have much trouble either. I went through a similar swap, (350 in an '86 in place of the 305) one Thanksgiving weekend a few years ago. Needed the truck back on the road Monday morning. These exhaust problems are what held me up. I ended up bringing a set of cheap headders and some pipe Monday night, and threw them in. It was a lot easier than screwing with the manifold/Y problem.
Good luck to you.