I bet the compression test wasn't properly done or a faulty guage was used. I don't think an engine would run on 75 psi, or at least it would run very poorly. Remove all of the plugs and use a known good screw in tester. Crank the engine until compression stops building. The majority of the reading should be reached within the first two revolutions.
Good luck,
Scott

Scott Ward

2 1948 1.5-ton Loadmasters
The red one and The snow pusher
1 1950 3100
1 1955.1 Chevy 6500
1 1954 Chevy 6500 2-Ton
1 1955 1st Series COE 5700
1 1963 K20 (454)
1 1964 C10 (350)
1 1951 1.5-ton Dump Truck
1953 and a 1956 Ford F800

Raising a teenager is like trying to nail Jello to a tree!