This is the replacement for the '71 only flat-top piston I believe. Will go easily into the 9:1 range with X/J etc. heads if you deck to 9.58" and use the Mr. Gasket .026" gasket. I have a set of original factory '71 pistons that I've used in 3 different blocks, the original block, a '79 and now a Magnum 5.9 block (using the '71 crank and balance factor). With the Magnum heads, it's in the upper 9's for compression by my calculations. Dead thread, but a search of the 2380P part number lead me here. LOL