71 383 - options

What changed from '70 to '71 to change compression is the height of the piston from the wrist pin to the top of the piston . Headwork and cam will give you the best return . The M.P. selection of cams are about the best cams for street use. Use factory valve train parts with it . Your heads are fine (open chamber). Closed chamber are 915 (closed chamber , 78.5 cc chambers). They are getting hard t o find and expensive . The cutoff point on iron heads is about $650.00 . Above that go with aluminum ones .