I'm still going to build mine. The price may scare you guys away though. I'll hopefully have a price this week.

I'm going with a 1 1/4 -12 shank with 1 inch bore. With Kevlar Teflon coated inserts. (High strength ends)

You can go with a smaller bore and still make adapter bushings for the m14 subframe bolts.

BUT from ball centre to arm end was 2.5" on my arm. And I had horrible toe in. So to have enough thread engagement you are pretty much stuck with a 1" bore end with 4 1/8" bore centre to shank end. That should give around 1.5 inch of thread engagement.