I having a custom stock bulit for my pre 64 model 70 and curious about the opinions on after market bottom metal (blackburn, williams, etc) Is there one that is clearly better than the others?
Availability is going to be your biggest hurdle. Williams is mostly Vaporware made from pure Unobtainium..
Swift Bullets bought out Blackburn and I would try them first.
I would throw Duane Wiebe in as well.
Having visited Ted a number of times at his shop, and having owned a number of his bottom metals, I would be partial to a Blackburn if they were still being made by Ted (may he rest in peace). If you think you would like the Blackburn, make sure that you can return it to Swift if its not up to your expectations for quality. And if not, go for the Wiebe.