Trader - some very good advice above. Measurements are important, as you already know but don't get too stuck on them. A couple of inches too long in a wheelbase is easy to fix. A couple of inches too narrow or wide in track width may be fixable with offset rims.
I did a '52 with an S-10 4x4 chassis. Still working on it actually, but real life is getting in the way.
I changed wheelbase and track width on my project enough to make it work.
I was really concerned about my project becoming "two piles of junk." This is a common problem, especially with people new to this kind of work who tend to bite off more then we can chew. I'm not much of a quitter, in fact I'm belligerent enough to finish something when I should have dropped it long ago.
The best advice I can give you is to keep your vehicle mobile as much as possible. This isn't the way a lot of people do things and creates a little more work in the long run. On the other hand, you don't have an immovable heap in the garage that discourages you every time you look at it. Just get it driveable as quick as you can. From the day I started stripping the donor to the day I was driving it (street legal!) was 2 months, 8 days. You don't need it street legal if you're just moving it around your garage.
Initial issues you're likely to run into are: repositioning frame mounts, frame-to-floorboard clearances, front sheetmetal/radiator/bumper mounts. Solve those, and you're laughing. Kinda.