CamaroMan the 2.5 is the chevy II motor. it was the 153 cubic inch little brother to the 196 inline 6 that became the 196/230/250/292 family. it had a 3.875" bore and a 3.25" stroke. it was essentially half a 307
it never was the pontiac motor (nothing common other than some bolts between the two. the poncho 2.5 was a 4" bore, 3" stroke halve of a pontiac 301)
the 3.0 is a bored/stroked version of the chev ii motor
achris yes technically the rings would be from the 350 with a 4" bore. the 305 has a smaller bore (3.736")
the pistons are different (or at least they were)
the piston pin is higher (closer to the piston top) than a standard 350. because the stroke is longer than the 350, however shorter than the 383. any good piston company will have pistons for the GM industrial / marine 3.0 ready for sale. any good rod place will have rods too
just need to know what your bores cleaned up at 0.020" over 0.030" over or 0.040" over prior to ordering pistons
FWIW, complete rebuild kits (assuming you didnt toast your rods or crank) are as low as $400
also, the 3.0 came with either flat-top pistons (some mercruiser and most volvo) or dished (most mercuiser and OMC) . check prior to ordering.
