Are winters' ring & pinion compatible with a DMI bulldog rearX-1?

Yes, both Winters and DMI buy their R/P from the same manufacturer and are interchangeable.

Thanks for the response. Another question. When I put the pinion in the case, and everything cooled, it was very, very difficult to turn the pinion shaft. I only had 'hand-tightened' pre-load on the bearings before installation into the case. How much resistance should I feeling once everything is cooled? Very nervous about this assembly.

Tighten the pinion nut after installation in the case. Nut torque is around 20 inch pounds which is a little more than hand tight. The pinion should turn easily.