There is no such adapter. You will have to make new side motor mounts for the 250, new mounts for a more modern trans etc etc, LOTS OF WORK!
It can be done if that's what you really want, much simpler to rebuild that 235.


It's easier to get forgiveness than permission!
1946 1/2-Ton Chevy
1953 Chevy 3/4-ton Factory Stakebed