A '61 235 or 261 would have a valve cover held on by four bolts in the lip. A '38 motor and any pre-'54 Chevy inline, would have a valve cover held on by two nuts along the top of the valve cover.
Making a '61 run on 6-volts would not be a real challenge provided you had a 6-volt starter and generator and associated stuff.
Let me tell you of a choice I made as a response to your dilemma about what to do.
I have a '55 1st GMC Suburban that is heavy on the patina where it isn't rusted completely away. It is a reliable driver and I've made few changes beyond making sure its safe and sane to drive. I've bought pretty much every patch panel Ray Stanley makes and a complete parts Suburban to get some pieces he doesn't.
But I'm not working on it because its a driver and its fun to drive AND its the only old truck I have that I can say those two things about. Someday I'll take it off the road and work on it, but not while its the only one I have that runs and drives.
I think being able to have fun driving an old truck is an important part of keeping me motivated to work on my other projects. I know you're leaning the other way but I find taking a drive in the Suburban renews my enthusiasm every time. Its not that its a Suburban, but that it drives.
If I were you, I'd work on the Suburban precisely because the 38 is still fun to drive. That also gives you more time to learn about the 38 and the wrecker body.
Just my two cents, the trucks belong to you...
