back about 15 years ago, I picked up a magnum 318 with a spun main bearing for like $200. I took the original 318 that was in my '85 5th ave that had about 65k miles on it, reringed/bearinged it, had a 5angle VJ done on the magnum engine's heads, home bowl port and gasket matched them, used the MP .028" thick head gasket, and had the '85's roller cam sent off to Bullet to be reground to the lobes I specified in my post. reused the stock magnum rockers, used hughes 1110 springs and 2.2L mopar retainers, and found the proper length pushrods for it from summit. back then on moparts there was a jig floating around to redrill the mag heads to LA, I think I used that.....I may have had ~$1k into that long block. took the headers/intake/carb (hedman, RPM air gap, 600CFM edelbrock electric choke AFB) that I had on the 360 I had put in my 5th ave and put it on that 318. it ran just as hard as the 360 (reringed shortblock with bowl ported/gasket matched 1.88" valve heads and a comp XE262) but with better low end response and much better fuel economy (like 20-25% better).
honestly, instead of throwing $$ at a 70's 318 with a cam/headers/intake and those poor flowing heads, it might be worth looking for a good running magnum 318 as a starting platform if you can pick it up for a couple hundred bucks. hardest part would be redrilling the heads to LA intake pattern unless you're OK with running one of the $150 chinese knockoff air gap manifolds
https://www.amazon.com/dp/B0BW8XLRGD?tag=fabo03-20...