Re: 350 heads on 305
As far as the head gaskets, they are all made to be used with the largest bore for a smallblock, which I beleive is 4.125. At that point, the cylinder walls are a little thin for my taste. They are made that way for ease, because rebuilds are always .030 over bore. Otherwise you would have about 20 part numbers for the same head gasket.
As far as the heads, putting 350 heads on a 305 will lower the compression, due to the larger chamber. This is the OPPOSITE with 305 heads on a 350, but 305 heads usually kill what little flow you had, due to the smaller valves. If you have 882's, I would have them checked for cracks, then put 202/160's in them, and go. Alot of guys are using the vortec heads now, and they are cheap, and give alot of go, but also requires a plumbed EGR, and a special intake for the new 8 bolt pattern. Edelbrock sells all the intakes, and you can get a set of heads for about $500 bucks.