Yeah, dried up power filter caps is usually the culprit on old units, would definitely need a battery holder too. For the noise mod, you replace the 3 caps that are tied down with zip ties on the main board, and there's 3 caps on the tube board for filtering. Noise mod also includes replacing 2 op amps on the main board but I don't think that's a major part of it, mostly just the cap job.
You can look up the guide on adadepot, the old board is there for archiving purposes, just can't create an account or post. There's a section there called the vault which has everything you'll need.
And if the only reason you don't want to sell it is because you think it's a lemon, I'm cool with it since the sole purpose of me buying it would be to rebuild it If you want to keep it for other reasons that's cool, I just like tinkering with shit.