Take a look at how greg built his D8
http://rctruckandconstruction.com/sh...ht=greg&page=3 Start with Post #59, don't worry about high drive, the inside's are the same. These are the motor's that Greg used, I bought some for a 1:8 D4h that I haven't started yet.
http://servocity.com/html/25_rpm_offset_gearmotor.html
Cheer's, Neil.