The 1967 axle used mono-leaf springs. 1968 and up used multi-leaf springs. The only difference is the spring perches, and those can be replaced as long as you have some welding skills.
I knew a guy that used a '67 rear in a '68 and he just used longer '68 U-bolts, and stacked washers between the perches. Not the best idea, but he got away with it.
The Chevy companion flange may be different too, but I remember there being a special U-joint that was half Chevy and half BOP.
any first gen F body will fit Second gen 8.5" also fits
While the second gen does fit, it is not perfect. The angle of the spring perches between first and second gen is off by a few degrees. You can force it to bolt up, but this puts stress on the springs and shackles. A better way is to cut the perches and re-weld them properly. I know because I have a 1979 disc brake rear in my 1968 convertible. We cut the mounting perches from the axle tubes, then lowered the car down so we could see where the spring perches rested on the '79 axle. It was off by a small amount. Then we tack welded the perches in place, removed the axle, and did a proper job of welding the perches permanently. At the same time we added the brackets for a set of 1967 dual traction bars.
The second gen rear is a Chevy C-clip type rear vs the BOP rear. You will definitely need either a Chevy yoke on the driveshaft, or that dual Chevy/BOP U-joint I mentioned. I believe Lakewood made it.
yes, a 67-69 Camaro rear axle will bolt right in, also a 68-77 GM X-Body car ( Nova , Apollo, ect ) the X-Body from 72 -77 will have the 8.5" rear axle, which is almost as strong as a 12 bolt and a lot cheaper to buy and can still be found in wrecking yards. If you go the 8.5" route, you will have to shorten the drive shaft one inch.
Heed old and ugly's warning on the monoleaf vs multi leaf perches. I'd skip 67 rears. There are plenty of 68/69 poncho firebird rears out there that will bolt right in. I dealt with a 69 rear that came in my 67. I finally put a 67 rear back in there and all is as god intended.
Another thing is the type of posi carrier. Every '68 8.2 posi rear I came across had worn out cone clutches. You can get brand new ones but that will cost a bundle, and they are still not that good. Meanwhile the 8.5 rears used disc clutches, which last a lot longer and are much easier to get parts for a re-build. Every 8.5 I have ever seen the clutches were fine. Even used 8.5 posi carriers from Gevo were in great condition, not needing a thing. On top of that, the gears sets available for the 8.5 is extensive, while the 8.2 in very limited. Do a simple search on this site: Yukon Gear I know it is a lot of work to adapt an 8.5 to a first gen, buy in my opinion, well worth it.
I have a 69 Camaro rear axle assembly on my 68 Bird, I was a bit pissed off when I discovered it was a Camaro instead of a BOP. I thought I'd grenade the Chevy rear with the torque of the 464/428, but it's held up, well almost, for the 18 years I've been driving it. I don't like the C-clip rears, I had an axle depart from a car once, the axle along with wheel an tire almost took out a Honda which was driving in the opposite direction across a 30 foot median, but this one has mostly held up, with one exception. Spacer shims came loose and the axle splines started to grind metal. I had to tear the whole thing down and redo it. I added a girdle cover to it at that time. One thing about the Chevy rear that was an unknown to me advantage, they are 1" narrower than the BOP. I was able to get the wider tire on without it rubbing on the fender lip.
