Yeah, I've looked into it.
The TR6060 is very similar to the T56 Magnum box.
A TR 6060 can be had from a wreck for notta lotta dollars. But then you may have to go shopping for a T56 Magnum mid plate. And also work out the shifter.
It's important to note the T56 and the T56 Magnum boxes are totally different animals - the T56 is quite different internally to the T56 Magnum, but the T56 Magnum is almost identical internally to the TR 6060; the T56 Magnum is the aftermarket version of the TR 6060. Tremec only used the name "T56 Magnum" for that box for marketing purposes, since people were familiar with the name "T56". But the 6060/Magnum gears are different (bigger) than the T56, and there are other differences.
The hard part is getting a TR6060 with a separate midplate and removable bellhousing, since many versions of the 6060 were often fitted with the bellhousing and mid-plate as a single part. But a T56 Magnum mid plate will fit on a 6060. Then it's a matter of making / fitting an adapter plate for the T56 Magnum mid plate to fit on a Volvo bell.
The mid plate is necessary because it forms the front cover of the gearbox. When a single-piece bellhousing is removed, the front cover of the gearbox is also removed.
There are kits available to covert the gear shift mechanism of a 6060 to a T56 Magnum style, which also includes adding a speedo drive.
But as Spac pointed out, the very tall 0:50:1 6th gear makes it pretty useless for Volvo applications. That is, unless you're running an ultra short diff ratio,