345014.....454.......70-86...
346236.....454.......75-76...2-bolt
359070.....454.......70-90...
361959.....454.......73-90...2 or 4 bolt
3963512....454.......70-76...2 or 4 bolt
10051107...454...............4-bolt, Bowtie, MkIV, 9.8" deck
10069286...454.......90-91...4-bolt, Mark IV, Short deck
10114182...454.......91-up...4-bolt, Gen.V
10185050...454...............4-bolt, Bowtie, Gen.V, Short deck
10237297...454.......96-up...4-bolt, Vortec 7400", "L-29" Gen.VI
12550313...454.......91-up...4-bolt, Gen.V crate motor, Gen. VI 4.25" bare block, fuel pump boss
12561357...454.......96-up...4-bolt, Gen.VI
14015443...454.......87-90...2 or 4-bolt, Mark IV, Truck, Motorhome
14015445...454.......78-90...2 or 4 bolt
24502504...454...............4-bolt, Bowtie, Gen.V, Race prep, 9.8 "short" deck height
The numbers in bold will be on the driver's side of the block, right by the bellhousing flange. There should also be a "GM" cast into the block in the same area.