looked at this while comparing my 250 to 350 donor truck. Other than the trans cooler in the th400 model the radiator of the C20 is the same dimensions tank and core as the 250 engine had and yes both are still genuine GM parts.
into this swap myself, found the mount location to bellhousing is shallower in the v8 than the 6 by 1/4" - 5/16". Working with the SM465, hopefully there is room on the cross member and trans mount to shuffle up to the v8. 1984 K1500 pickup had to 250