need advise in a 318

Most of the info above is right on. All 318 heads are closed chamber though, not just the 302's. Pre-'72 318's should have a forged crank, so will most truck 318's. Most of the rest are cast. But other than that they're pretty much all the same. Compression changed a little, but if you're rebuilding it won't matter.

For a rebuild, up the compression. 318 pistons are notorious for being further below deck than they're supposed to be, so check. 302's are good heads, but stock magnum heads ('92 up smallblocks) flow better and are also closed chamber. You'd need a magnum bolt pattern intake and oil through pushrods and lifters to convert over, it's covered here already. But get your pistons close to zero deck, your compression between 9.5 and 10:1, with stock magnum heads, a good cam and headers and you'll be over 300 hp without trouble.