volvo diff

I was advised to run a Volvo diff in my Mk2 rally car and was given the following info by a fellow competitor with a vast knowledge of Volvos.
"Most 140s and the early 240 diffs are basically Dana 30s. These diffs are used in the front of many Jeeps, so they are well supported in the aftermarket.

Ratios range from ~5.4:1 to 2.xx:1. A good Volvo motor will break a 5.1 in time, but an Escort probably won't have that problem (less weight, less torque, less power). If you really need a short ratio and a super tough diff, then a 1031 conversion will work - but the bits have to come from Sweden and are about four times the price of the American stuff...
Standard Volvo ratios are 4.56, 4.3, 4.11, 3.91, 3.73, 3.54 and possibly taller.
In Volvo world, 4.56 and 4.3 are impossibly rare, 4.1s and 3.9s are the most common.

LSDs are available - mostly either Detroit lockers or Torsen style, rather than the plate-type.

Under 300hp, you won't break one. Beyond that, the cross-pin that holds the planetary gears in place will flog out and break (like early Mazda diffs do). Like a Mazda diff, if you weld the pin in place (or turn it into a locker, or fit an LSD), then the problem goes away.
The next weakest point is the axles - big power and sticky tyres will twist the ends off. But we're talking tar, 350+hp and a fair bit of time before this is a problem.

Most Australian suppliers are hopeless and/or stupidly over-priced for ratios and LSDs. The one exception is Wooder's Garage in Hornsby who will sell you a ratio for only marginally more you can get one from the USA. I paid $350 for a 4.56 for my Volvo. They have the ratios in stock, and they're easy to deal with.
Look at ~US$500 + freight for a Torsen.
The diffs themselves usually sell for $50~100, disc to disc.

The very early 140s (rare in Australia) ran a Dana27 which you want to avoid. I think the change-over was mid 1968, and possibly corresponded with the change to the 2-litre engine (B20 vs B18).
The later 240s ran a Dana30/Dana44 hybrid. These are known as 1031s in Volvo-speak (the early 240 diff is a 1030). The change-over is in the late 1970s - but there is no hard-and-fast date for the change-over.
There's a lot of incorrect info on the internet about "single rib" and "twin rib" relating to 1030 vs 1031 - ignore it. AFAIK, the 1030s have a brass plate riveted to the nose of the diff, while 1031s have a sticker on the rear of the LHS axle tube. I'm not saying this is 100% correct, but it is better than the twin-rib nonsese.

Standard stud pattern is 5x108, FWIW.
Decent sized discs with twin piston iron calipers, and internal drum hand-brake.
Housings are tough, but not indestructable - my gut feeling is that an Escort rally car wouldn't need the housing to be braced (esp as most Escorts manage an average of 25km/rally before breaking down... ).
240 diffs are narrower than 140 items - but not by much. Most of the Escort kiddies go for the 140 diff."
Looks like you will need to be running bubble arches.