That's a tough one. Warmoth is among the more reliable suppliers of quality necks, but this approach of replacement would probably be much more easily embraced by your friend if he could find someone able to finish out the neck to more accurate historical specs and vibe. I wish I had a recommendation for someone in the area who could meet this demand, perhaps someone else here knows and will chime in. If not, you may find a more ready source of referrals over on the TDPRI or Talk Bass forums.
Good luck, and I would pitch to your friend that setting aside the original neck (even with all it's flaws) may allow better opportunity to preserve its originality, and perhaps allow its proper restoration as more advanced and less intrusive techniques are developed in the future. Whether this outcome is likely or not I honestly don't know, but a lot of those necks can be so squirrelly that with methods known today there is no way to restore them without fundamentally corrupting their originality. If nothing else though, arguing the ethic of preserving components to someday allow for less invasive repairs with techniques not yet imagined, may make the compromise of using a replacement neck for now seem more psychologically bearable.
Good luck, and I hope he can find someone able to get the bass back in action again.