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Check the cc's of the heads and we can help you further.

If the 452's are equal to the 516's use the 452's. Reason being, hardened seats, 1.74 exh. valve, same compression, slightly better flow.

Ideally you want the compression of the 516's (w/the milled 452's) with the benefits of the 452's. And sounds like they are close.

If both sets of heads were equally worn and untouched, I'd update & freshen up the 516's. Just my opinion.

Cc'ing a set of heads can be as easy as putting some old spark plugs in, filling the comb. chamber with Play-Doh, cut the clay level with the deck surface, and then pull it all out and drop it in a beaker/measuring cup with a known amount of fluid. What ever it registers as a new amount is your "cc's".

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