Cheapest place to get BB/4speed crossmember
 

Any place might have a used one?

I have a BB/T350 and ive heard the BB/4-speed will fit.

Have you checked on ebay yet? You can get a brand new one for $120 shipped, Tamraz is the cheapest I've seen. I haven't tried cross-fitting one like what you're looking to do, but in the past I did convert a 69 with an automatic to manual and kept the same crossmember, so what you're hearing may be right. It's been so long though, I can't remember if I needed to do any fine tuning to the mount.

As far as I know there the same , I have changed both ways and never changed the crossmember !!