I realize the time, effort, and money it takes to build a custom bike... but 4k for an RD that needs a top AND bottom end?! It's very hard to expect to recoup the money spent on a bike built to YOUR tastes, bc style is so subjective. More power to you if you can pull 4,3, or even 2 k for it. I'm at the point where I have spent 4.5k on mine, and I am thinking if selling it for something modern but i know that 3500 will likely be my ceiling. And that's with 1200 miles on a fresh balanced crank, top end, and reshsped o ringed heads.
It may serve you better yo find a usuable crank replace the seals, spend the $350 for a top end and sell it running. Good luck with it