That original engine is probably a spray-oiler 235, which came out in 1941, an upsize of the 216 engine for medium-duty and larger trucks. Don't trash it- - - -your mechanic buddy might not be able to rebuild a Babbit-rod engine, but the mechanics I grew up around at my father' shop in the 1950's made their living doing it. Plenty of parts are still available, and there are still a few of us old geezers who know how to work with Babbit metal. It's also possible to bore out the rods and replace the Babbit with insert type bearings. The main bearings are already replaceable, and aluminum 235 pistons are a drop-in fit for the original cast iron ones. Currently, I'm modifying a Babbit-rod 216 by installing a pressurized crankshaft and aluminum pistons from a 235. It will be a 235 with full pressure oiling and a high volume oil pump that looks like a 216 from the outside. With different connecting rods and some creative stroke changing, a "216" can become a 258 cubic inch engine.
There's nothing wrong with the engine upgrade you're planning, but it would definitely be possible to rebuild the original engine if you choose to do it. Good luck!
Jerry
