Dennis, welcome aboard.
Since you asked about a banjo rear I suspect you intend to keep the transverse spring. Give the era it was built the front is the same spring set up? Your question about the open drive would imply you're planning to deviate from the vintage trans it may have?
There are a couple ways to convert the banjo from the torque tube to the open drive. The '46-7 Ford pick up trucks had a banjo rear with an open drive, To use that would involve swapping out the center section and probably some of the carrier parts, depending on what axle you have in the car now. These truck banjos can sometimes be hard to find, other times not......typical old parts. I have one out in the shop, but you're a ways away for that.
The other way is to use a kit that's made for the purpose. Kits are available from Speedway Motors, or Hot Rod Works: Open Drive Kits I would suggest the HRW one over Speedway, it's better made and they're good people. As you can see in the link, there are several options so you'll need to figure out what you have now before ordering.

Rebuilding the springs is not too tough, but remember that there's a lot of stored energy in any installed spring. Use a lot of care when disassembling to avoid injury. It's easiest to remove either spring from either axle if the entire assembly is out of the car. I've done it under the car because I have experience and I'm a dumb ass, but for a first timer I'd suggest pulling the axle assemblies out first. You'll have more working room and it will be safer. You'll need one or two high quality, stout C clamps or equivalent, Two things keep the spring in tension as installed. The center bolt in the leaf stack that holds the leaves together, and the shackles. I'm going to assume you don't have the special tool to spread the spring at the eyes to remove it from the shackles. It can be done without the spreader, but I won't go into that here or now. Again, it's an experience thing. The easiest thing to do is securely clamp the spring stack together, remove the center bolt going through the leaf stack, and then very slowly ease off the clamp. That will release the stored energy gradually. Once all released there will be little to no tension on the main leaf and the shackles can be removed pretty safely and easily (depending on rust). Depending on the spring and what modifications may have been done in the past, you should have somewhere around 10 leaves. The main leaf has the eyes with bushings (hopefully not all worn out), the rest should have tapered ends and be of gradually diminishing lengths. Depending on what you learn from inspection will determine what is needed to "fix" them. Often they are just dirty/rusty and a good cleaning will make them better. Look carefully around the center hole, they will often crack there. Any broken or sagging leaves can be repaired/replaced by an automotive spring shop. Most good sized towns have one, usually for the HD truck world, but they will work on lighter stuff too (the off road guys can tell you where those shops are). Putting the spring back together after clean up and refinish is the reverse process of above, but be extra careful as you're putting energy back in the spring when tightening the clamp, and bad things can happen if you're sloppy about it. Getting the center hole to stay lined up can sometimes be a challenge, but using a long piece of all thread, or even a rod would help till it's fully clamped for the bolt (preferably a new one) to be reinstalled. There are replacement springs made as well, and are readily available, so you have options there too.