Now im not positive but the 80 I think was their large 8 track and it will use 10.5 inch reels with 1/4 inch tape. It would be concidered their prosumer machine, it is twice the size and weight of a r8.
I have had 3 of the R8 fostexs and its a nice machine, It sounds good, Runs at 15ips has dolby c noise reduction. And its easy to carry if you want to take it some place with you.
As far as the real specs on them I cant help you.
I was in a band that recorded at a studio that used the 80 and it did a good job other than that, Thats about all I can tell you about it.
I think I would take the one that is in the best condition all around.
If im not correct on the size of reels on the 80 and it only takes 7 inch reels
than I would go with the R8 since its a newer unit.
Hope this helps and makes sense