307 V8 pistons are a drop-in swap into the 250, and they raise the compression a little if you get the true flat-top pistons for the 307. Some later model aftermarket pistons have a chamfer around the edge of the piston that doesn't give as much compression boost as the originals. Speed-Pro makes a hypereutectic cast 307 piston that I've used on several 250 rebuilds along with a little hotter camshaft, and the combination of the compression bump and the cam really wakes the engine up in the low to midrange area. It takes some serious cylinder head, intake and exhaust work to get much of a high speed gain.
Jerry

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