After pricing out various 8 3/4" axle components, and getting a bit of sticker shock, I'm wondering: How readily could one swap a 9 1/4" late model truck axle (Durango/Dakota) into our older cars?

Granted, you'd need custom axle shafts with a 5 bolt pattern (about $4-500), but the axle housing and gears are relatively plentiful and cheap. Furthermore, most of them came in very desirable gear ratios of 3.55 or 3.92 along with the Sure-Grip

Thoughts?

Well B bodies from 74 up as well as C bodies did have the 9.25 available, I've got one in my sig car. Seems to me it'd be much cheaper and easier to score one of those and put it in. If you're going through the time, money and hassle of converting a truck rear end over for your car, you might as well get a junkyard Dana 60 from a truck and convert that over. That effort on a 9.25 wouldn't really be worth it.

The 9 1/4 is a C-clip rear. I would never use it
in a car or truck where you plan on bangin gears
or any posi hard launches. Break an axle, and
out it comes. Unless you looking for 3.08 - 3.23
gears, do up a Dana 60 and never worry about your rear again.

If you must do a 9 1/4, then have the different
ends welded on. If you break an axle it stays
in and doesn't wreck your 1/4 panel.
Then you can run a 2.96 gear a fly down the freeway.

It really doesn't look like it'd be that hard to weld up a jig to keep the rear axle in place. If you have rear discs the rear axle won't go anywhere or fab up a little guard to hold the drum from sliding out in the even of a c-clip failure. Plus you don't hear about mopar 9.25 c clip issues like you do with the brand X guys.

You could always go w/ a Furd 9". I still think you can get a 8.75 case for $50 and a decent pumpkin for around $4-500.

I wasn't looking at any change to the axle housing (other than perches) because the width is similar.

By the time one builds and freshens an 8 3/4" properly, you might as well buy a built Dana 60.

However, I don't want quite that much unsprung weight under the back end of the car

what are you trying to do? A backbraced 8.75 is pretty strong. You can buy a new ring/pinion for around $200 and the clutch kit (assuming it's a 472) for $99 that should get you a pretty strong set up. Or you can look around and find a used pig for around 4-500. A Dana is about $1600.