The stamped # will peg it.
Block casting 3738307 is listed as,

1958-62 Passenger, Std & P.G., Hyd. Cam
1958-62 Truck, Mech. Cam, Front Side Mounts, Van 60-62 only
1960-62 Truck, Mech. Cam, Front Center Mount


-Tom

1950 Chevy 3100 w/ 1956 235