8.5" rear
 

Recently found what I think is an 8.5" 10 bolt. Having some trouble identifying it. It has a completely smooth round cover and the yoke is round looks like the tail shaft bolts on using bolts through a flat round plate, mount saddles line up with my 68 fire bird and its about 60" wide from flange to flange. the tail shaft flange mount has thrown me. Any ideas on what this may be

The housing is indeed an 8.5 X-body piece from a Seville, & originally had 5 on 5 bolt pattern axles. I have several Seville housings with pinions & the flat flange still in them...just core housings to build off of.

You will need the 3R pinion flange which was used on the majority of 8.5 rears. Should be easy to come up with pinion flange, even in Australia. If swapping from your early Birds 8.2 10 bolt rear, will need to shorten your original driveshaft 7/8" to 1".