Early GM posi question

I have a 60 Bel Air that I know I am going to want to set up with a posi soon. It is going to have a mild 454 with a standard trans. The original car was a 6 cylinder and there is no "P" on the third member, so I am assuming its not a posi.

I have been shopping for a "drop out" that I could easily swap, but they seem pretty scarce, so now I am looking at getting into the guts of the rear end instead. I have a few questions about early GM rear ends such as mine...

How many splines are in an axle such as mine? 28, 30?

What size is the unit? 7 1/2 or 7 5/8 or other?

How many bolts? 10 or 12?

Anything else I should be aware of when shopping for a posi unit for my rear end? I do know I have to modify (grind) my housing to accomodate a posi unit.

Sure, Ill get some, but it doesn't have a cover. Its a "third member" style, similar to a ford 9" (not sure what you would call these style axles). From what I understand, this rear end was in any late 57 - 64 full size or up to and including a 62 vette.
This picture is simalr, but not mine.
http://i1.ebayimg.com/01/i/000/a5/12/56c5_1_b.JPGhttp://i10.ebayimg.com/06/i/000/a5/12/5776_1.JPG

From what I have heard those units are fairly week when you throw alot of torque at them.
I'd look for a late 50's early 60's Olds rear. Although not a drop out style,it should'nt be hard to bolt in and these were the rear of choice for all those early Slingshots and drag cars.


Doug

In my old '56 Buick, I had that exact unit. Third member experts always said they could take a lot. When I dropped a 502BBC in it, it failed, not badly but an old school hot rodder told me what to do and it worked very well. We took the ring gear to the surface mill and knocked the lugs off. Built a precision fit spacer (not the aftermarket style you can buy), stepped up to grade11 bolts with GM loctite and the darn thing still runs to this day with a 540 BBC in it with not one failure. Just food for thought. By the way, the whole purpose to keep the OEM axle and member was for a touch of originality.