I would go with a 454 for sure. Dont get me wrong, olds are great motors But they have issues that need special attention. You would be better off spending more money building a chevy because they offer cheaper horsepower than the olds. You could find a good block from one of the guys on here and a set of heads cheap.Here is a idea of costs for a good 454 build up.
machining on the block $600
machining on the heads $300
Pistons$400
Bearings$120
cam kit$250
intake$100
headers$250
mounts$250
ignition setup$150
Carb$ use your old one!
Oil pan$200
timing cover$60
Driveline$75
that is a baseline for costs. Remember i am still drunk from lastnight so I might be off a little bit so bear with me.
Advantages with a chevy
1. reliable
2. more horsepower
3. everybody has parts for them
4.you can run them over 5k rpm's without worring
5.better oiling system
6. cheaper to rebuild.
So there is a little info to think about. I'm pretty sure with the help from a few guys on here we could possibly get you into a chevy for a decent price. We all have parts laying around
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