flywheel question

checking my flywheel ,just purchased car and have trans t-5 out and trying to verify correct flywheel, currently there is a 50 ounce 157 ,but i checked block numbers and is showing to be a 79 casting, ,has a serp setup like my other stock fox body, any sure fire way to see before new motor is ruined

my block casting begins with d9 which i think means 79 casting,, should this motor have the big 50oz flywheel, im ordering a new one since its only 8 bucks more than a reface.