327 OMC (SBC) from look of intake with "front of engine" fill tube and no PVC on the rocker covers....
Check casting number on flywheel end of engine and post the number...it will tell us immediately what it is...
BTW...most OMC 327 are 4 bolt mains,,,,,
Check them really well for valley cracks...these get left out in inter weather with zero freeze protection...
