Thanks Nick for the reference. I did replace a Mark VII headstock with a Mark V headstock. There are several people that own and play with the Mark VII. One is Farmer at firstname.lastname@example.org
who has a collection of them. Another person is at http://www.califsawdustman.com/
who I believe had some Mark VII parts for sale last year. Bob Fulwider (Email = bobrepairs85@sbcglobal Phone after 1000 PST - 775-828-0957 ) had a lot of Mark VII parts for sale last year. I have only done repairs on the Mark V and 10E/10ER Shopsmiths at this time.
Other than the different Speed control setup, it's pretty much the same as a MarkV. Same Quill and drive sleeve (Poly-V), control sheave assembly (only there's the follower out the end instead of the clip), A reversible motor is advertised but both Mark VII I have seen had only an on/off switch. If it has a reversible motor that works, it is worth the $300 for the unique motor capability.
One other major difference is the crank for headstock movement. There's a rack/pinion setup for moving the headstock on the ways. This was removed when using the Mark V headstock.