I can't remember the bore sizes of early HEMI stuff but at 4.250 it sounds like a late HEMI size. Late being Gen II HEMI.
The measurement issue is the clearance is built into the piston. If you have a nominal bore size of 4.250 then the piston SHOULD measure 4.244-4.245 for a piston of that era. If the piston actually measures 4.250 WITH A MICROMETER AT 90* TO THE PIN BORE PARALLEL TO THE PIN, then the nominal bore size would be 4.254-4.255 and that's an ODD size.