While you may be able to rering your old pistons or maybe a 0.010" overbore would be sufficient, you will find the best (lowest) prices for an overbore of 0.030" and pistons will be cheapest on the 0.030" oversize (usually). New cam bearings are a good idea and new rockers and pushrods are not that expensive in the overall scheme of things. Why not add new Z28 springs to the heads and maybe shave the heads a little so the surfaces are flat and raise the compression just a bit? I would suppose it is easy to get a 3-angle valve job on your old valves as long as the seats are OK. While the heads are apart the cheapshot enhancement is to smooth out only the exhaust ports but not bother with the intake ports to maintain good fuel mixture. There are a number of inexpensive rebuild/overhaul kits available under $300 once you accept the 0.030" overbore idea; boring and honing might be about $8-10 per cylinder.

Don Shillady
Retired Scientist/teen rodder