That ain't maple, that is a disaster! I would avoid any neck that has been disassembled and had the truss rod yanked, if only because the guy is selling as is. Who knows what went on there, but I would not be surprised if it had worse inherent neck-twisting than what you have now.
I agree that maple fretless board on 60s vibe P basses is aesthetically wrong. I would want a 70s TV logo'ed B neck on there. If I were out to for something exotic I would look for the early to mid 80s Fender Japan fretless Jazz necks, which had a cooler vintage look to them, as long as the Jazz Bass decal didn't bug you. They show up on the ebay often enough, and to be completely honest they are a great bass in total. If you found a nice one of those, sell the RI body and make more cash. Certainly a sleeper on the market, as is all 80s Fender Japan bass stuff. Ok, not the Bullets and 32" scale P basses. But in terms of bang for the buck and intense outsider cred, 80s Fender Japan is the Gibson bass of Fender.
I am sure the fretless Fender Mexican stuff is fine, but like fretless US necks of the past few years, cheater lines are for kids.