I have 308's sitting here and I went with the magnums. It is more work, pushrods, adjustable rockers, valve covers (rocker adjusters hit baffles I used late LA covers). My exhaust manifold on the drivers side needed 2 gaskets to seal. I think the magnums are more work but I like them. The pushrods I used are from a magnum motor, I picked up some Chevy 1.6 stainless adjustable roller rockers and edelbrock guide plates. The guy that built the (new) bare castings used 7/16ths screw in studs. The motor runs well, I'm still tuning it. Its a little lean on the primaries. The 308 heads would have been less work but the magnim heads are a better head in my opinion. I did start with brand new bare castings. Good luck, I hope this helps.
