The two different radiators require different mounts. The v-8 lower mounts sit on the upper part of the cross member and has an off set upper hold down that's different than the one that would mount the six cylinder's. You may have to go junk yarding to get that upper hold down, unless it's available in the reproduction world,
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!