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So if you're running coil overs, that mount behind the rear axle, and they mount to the frame behind the rear axle, haven't you just cut all the strength out of the frame?
This one is getting dropped off at a engine builder when its time. If the block is good enough its probably going to 427ci so everything but the block and maybe the pulleys are gonna be replaced. I may clean the old pulleys up and paint or get them chromed, Not sure yet. Probably AFR heads, high lift short duration cam, and forged internalsKeep in mind that 351's all had 28.2 oz imbalance cranks when you get the flywheel. 70's distributors had slow/retarded centrifugal advance curves so recurving it will make a huge difference. I assume you'll be rebuilding it, a 72 would have had a silent timing chain and nylon tooth cam gear, both of those fit nicely in a scrap metal box. I think a 72 used rail rockers, if so you'll save valve guide wear by using hardened pushrods and guide plates. Better heads would be a bigger improvement, even stock E7TE heads.
As much as I want and would like to save money..... I am always planning for the future of the engine. Just like with my rangers 5.0 I got the short block built to handle a blower even though right now its just P heads and a letter cam. But I have a top end kit that is more for boosted applications from trickflow with the head size and cam. And I have a blower on my mustang that will be collecting dust once the 363 goes in that. So the blower is going on the ranger and the mustang is staying N/A and this roadster since its a fair weather car it will most likely get a 671 blower at some point. The builder will know what needs to be done even if its a lower compression 427 or 408 the same way the do a low compression 347 its gonna run like an animal even before the blower is on it.A 72 block should be OK, 302's got .023" extra deck height from 73-6 to sink the piston in the hole and lower compression and I think 351's might have as well. If you're not going to rev it beyond 6k, hypereutectic pistons are lighter and can be fitted tighter to avoid cold engine noise. And as a bonus they're cheaper so you can use the savings to convert to a roller cam, conversion roller lifters aren't cheap but they're worth it.
I may have to build a street rod after all, watching your progress got me interested again.