I'm leaning toward a 283/327 swap
If I was going to put a V8 in mine it would be a 327, best SBC and first fuel injected engine to be built. The 283 is it's little brother, probably gets better gas mileage, but less power. But I'm keeping the 235 that was put into it before I got it.
I've read here somewhere that Nova or Camaro rear ends will work with the '40 frame.
Your frame should be like mine, I have a '46, which was the same as the '41, and I'm pretty sure there isn't much different on yours sans the grill and light differences.
I found a '55 Series 2 rear axle and using it so I can reuse my wheels. If you plan on getting new wheels, those camero and nova rears typically have 5 lug 4.75" diam pattern on them.
S10 will work well in your truck also, most likely the 2WD, the 4WD is about 4" wider and people use those for the AD trucks, but those truck are also 4" wide fender to fender. Another I've seen both rear axles and front clips is from a corvette. And if you get lucky on one of those it will have disc brakes, probably not as useful on the rears, but couldn't hurt if you plan to get with disc brakes on the front as well.
