I recently purchased a started project....
8 3/4 rear from supposedly truck was narrowed & axles as well
need center sect unit???? Which one should I seek?
Plan on using 727 hooked up to 360 (1977 old camper mtr)
in my 37 truck. Posi would be great. I measured axle shafts dia and got 1.5" approx?
just do not know which way should go?

The 742 is stronger than the 489 cases are stock, if you replace the crush sleeve in the 489 it will last a lot longer under abuse than it will stock. It will still not be as strong as the 742 is due to the differences in the sizes of the front pinion bearing and the diamerter of the pinion gear shaft where the front pinion bearing rides

ANY 8.75 case will work, they all have the same spline count/axel shaft size, unless they have been modified.

For a 360 in a light pickup it doesn't matter. Any 8 3/4 center will do the trick.

I'd pick in this order:
1. Ratio
2. Sure Grip or not
3. Case casting number

If you're talking about a limited sip differential in a Chrysler Corp car, their trade name is Sure Grip.
Positraction is a General Motors trade name.
Mopar people get bent out of shape pretty easily if you use the GM term. Another example is "broadcast sheet" which in GM-speak is "build sheet"

It's kind of fun to learn and use the correct terms because it's like the club secret handshake.

R.

Don't let anyone BS you into thinking a 741 case won't hold up. I have run dozens of them behind mild 440's, run them hard and never had one fail. The factory used them behind Max-Wedges. With a small-block, any of the cases should hold without a problem.

There is nothing wrong with a 741 case, but the factory never installed one in a Max Wedge car.

Really? What did they put behind max-wedges? I read that they used 741's, but I know what you do for a living, so I won't argue! lol

Just purchased a 742 case...on its way
still seeking internals??

any 8 3/4 as long as you don't plan on alot of HP and hooking up....burning rubber won't hurt any.......to a point

Max Wedge cars came originally came with 742 castings.

I'd get a good used clutch (741/742) sure grip pig in the ratio you want & throw it in there. I twisted the pinion splines on a 741 behind a circle track 360 but in your app you wont have a problem with a 741.

www.doctordiff.com
Is the place to get internals. I'd vote for a TruTrack limited slip and whatever gears you want to live with.
Heck, ship him the case and get it assembled. It's worth the cost to have it done right.
R.