I agree with the others that it would be best to find a good GMC motor like a 270 or 302. But as Mike mentioned, I'd just drive the 248 for a while until you find your match.

However, if you are determined to install a 235, there is how 49geezer installed a 261 into a GMC 1/2 ton

Plate

SWEET
Sergeant At Arms: Old Dominion Stovebolt Society
BUNS?!?!?!Where we're going, we don't need no buns.....
1950 GMC 450
1951 Chevy 1/2-Ton
The GreenMachine
In the Stovebolt Gallery