Fink- When I did the conversion on a 57 about 5 years agoI bought the mounts as shown from one of the vendors. I think it was about $80 at the time.
I'm pretty sure the only difference is in the actual block mount on the top. If I'd known that before I ordered mine I would have had a friend fabricate a set for a 6 pack. If you can weld 1/4" plate and drill 3 holes you can make a set using your existing 6 cyl mounts.
Devin
