Nathan,
I wouldn't recommend that you go thru all this work and reinstall the original tank. We were also faced with replacing the STBD tank the first year we had Namida. Not exactly something that you look forward to on a very hot and humid August day;-) Good news and bad news (sort of)... First, Bud is a great resource and can get you the tank you need. I found that his pricing is actually cheaper than if you went directly to the guy who makes up the tanks. With any luck, you will only have to change the tank once, so take your time and do a good job. The tank you install will be aluminum (regardless of what you took out). The secret to a long tank life is to keep it from sitting in water, keep water out of it, and ensure that it doesn't become a catalyst for stray currents / dissimilar metals. Installing some rubber strips under the new tank on installation (tack in place with some 3M 5200) will keep water from collecting under the tank on the shelf. Be sure that the tank is grounded and finally keep it full of fuel as much as possible to minimize the amount of air space in the tank for condensation.
Now for the not so good stuff. Namida has a Perkins 4-108 which makes the squeeze a bit tight, but I was able to remove the old tank and install the new one with a minimim amount of equipment removal. If I recall correctly, I had to remove the mushroom air intake (for the Perkins) and a set of house batteries that I have on the STBD side. It takes a bit of turning, twisting and pushing, but it will go in. Not a case of just unbolting it and heaving it to and fro. Depending on the equipment you have, your situation may be different. I was relieved to discover that I didn't have to disassemble or remove the engine to get it in..
Good luck. You will feel quite a sense of accomplishment when you finish.
Now, when you are done, install a set of tanks in a W42.... There's a real project;-)
Mike & Jenny