Here's one member's results of the other way around on the 10-12 deal.
http://www.***boat.com/image_center/...0/SUC50296.JPG
OUCH!!! That'z a NO NO.................
Only same gears work in same case. 8*gears- 8* case, 10*gears-10*case, 12*gears-12*case, 0* gears parallel-0*case parallel.