I just purchased a 200-R4 for my 1968. I think I plan on using my stock turbo 400 cross member.
I know with what little research I have done this cross member has been recommended.
http://www.bowtieoverdrives.com/cata....php?ITEMID=56
The B&M lock up box you listed is the same one that I purchased. But, I think they are all on back order for at least a month.
The B&M mega shifter I think will only have the detents for for the normal three gears. Newer ones might be different.
I am running a stock shifter and I purchased a kit from Shiftworks to replace the original detent.