Lots and lots nad lots of little things mean there are no off the shelf pistons. Frisntance, the Mopar rod is 2.0" at the bearing, 1/8" smaller than the 2.124" of the stock 250 rod.
The 265 Hemi piston pin is 15 thou bigger on the Hemi than the Ford item, but it is also the same as the Chevy small block
Any of the pistons from pin centre line to top of piston need to be 1.66 inches tall with a Chevy wrist pin, and can't be any bigger than 3.74". The stock size 245 pistons are 3.76", but you have to overbore 80 thou and find a set of brand new 245 pistons. They are too tall at 1.77".
Perhaps the best option is the 253 Holden piston is 3.685" in +60. It is 1.75" tall. If you hone a mint stock block 250 out 5 thou, and add a 62.5 thou turbo head gasket and two 41 thou thick ACL gaskets, you could run either the 253 or 245 pistons without having them hit the head.
There are various Subaru 2.5, Chrylser Voyager 3.3 and even some odd ball Y-Block items around. Samll block Chevy ones are not easy swaps either.
Summary is look at these
200-221-250 Aussie Falcon 3.68" bore, comp height 1.535"
245 Hemi 3.76" bore, almost too big, comp height 1.77, almost too tall
253 Holden 3.625" bore, +60 okay, comp height 1.75, almost too tall
265 Hemi 3.91" bore, too big, compression height 1.77, too tall
400 Chevy 4.125" bore, too big, compression height 1.531, too shallow
350 Chevy 4.000" bore, too big, compression height 1.531, too shallow
327 Chevy 4.000" bore, too big, compression height 1.675, perfect
307 Chevy 3.875" bore, too big, compression height 1.675, perfect
305 Chevy 3.736" bore, perfect, compression height 1.531, too shallow
302 Chevy 4.000" bore, too big, compression height 1.800, too tall
283 Chevy 3.875" bore, too big, compression height 1.800, too shallow
267 Chevy 3.500" bore, too small, compression height 1.531, too shallow
265 Chevy 3.750" bore, too big, compression height 1.800, too tall
262 Chevy 3.670" bore, oversize okay, compression height 1.75, too tall
