You have kind of picked a combination that you may not be too happy with (don't ask me how I know). Like what has been said before, a truck is a bit heavy to realize any performance mods that you might install. You are going to wind up with a gas hog that you can't afford to drive that very well might be a dog. One thing that I might recommend, if you have a Pull-A-Part junk yard close by, go and spend some time checking out some of the later model trucks that you might find there. Sometimes you can luck out and find a pretty decent engine for less than $150 with all the accessories on it.
The last engine I bought was out of a 97 Tahoe 4X4. I dropped a 383 stroker kit in it and that particular block took almost no clearancing for the crank. You can get a 377 kit for it also. The only difference between a 383 and 377 is .030" bore. The best thing about the later model blocks is that you can find one with 200,000 miles that you might be able to get by without boring. Because of the hypereutectic pistons and the low friction rings, I have found 350 blocks that I could still see the factory hone marks on the cylinder wall that had well over 200,000 miles on them. On top of that, most of them in that year range should be factory roller cams. You can buy a decent roller cam reasonable sometimes, new and used. The roller cams do not wear like a flat tappet cam. The factory hydraulic roller lifters have been known to run for 750,000 miles.
You can also find used factory high performance roller cams pretty reasonable. The reason I mention this is I went through the same thing you are talking about. I bought a brand new 1977 Chevy Cheyenne and pulled the engine with less than 500 miles on it (absolutely STUPID). I put a small block 400 in it, bored .060, 12.5 compression ratio, high performance cam, aluminum intake and a nice new Holley 750 carb. It absolutely sucked. My gas mileage went from 11 MPG to about 6-7 MPG and I hardly noticed any improvement in power at all. It pulled heavy loads a bit better because of the longer stroke of the SBC 400. You could not hold a gun on me and make me do that again.
You will get a better performance gain and better fuel economy by installing a factory roller cam 350. You don't have to take my word for it, if you are bent on doing this, you will remember what I am saying here. Back when I did that, I thought I was smart and no one could tell me any different. I am smart enough now to realize I wasn't so smart at the time.

Ed