Recommend Head Rebuilding

The 308's are an open chamber smog head with 360 sized ports, but had redesigned exhaust ports that flow quite a bit better than earlier designs. Kind of a precursor to the Magnum head exhaust chambers.

They can be made to flow as well/better than the earlier heads, I have a ported set of 308's on my 340, they flowed 264 cfm at .500" on the intake side on my machinist's flow bench. In stock form they're pretty comparable to 1.88"/1.60" J heads, just with slightly better exhaust flow #'s.

But, for a stock bottom end 318 I don't think they're the best head out there. 302 heads would be a better choice, they're closed chamber and have a similar design exhaust port. They have the smaller 318 ports, but for a stock 318 that's a good thing to maintain port velocity. The 308's will lower your already low stock compression because of the open chambers, and the large 360 ports will reduce flow velocity.

For a 318 with aftermarket pistons and a hot cam, I could see using the 308's, or any 360 head for that matter. But for a stock bottom end with ~8:1 compression, the open chambers will kill your compression. The 308's would need to be shaved pretty significantly to get the chambers small enough to maintain or improve your compression ratio, as the 308's chambers are 65-72cc's depending on the casting.

The rest of your build seems fairly mild. Not a bad thing, but the 308's will be overkill in a big way. The compression ratio is going to be a big issue with a stock bottom end and those heads. What are your plans for the car? Just wake up the old 318?