As for the car here, I would want to know a lot more about the spec before bidding. Seems to be a lot of chatter in the comments about the spec and how much of the original car is actually there.
I don't know about the APRC, but Group A was basically gone from Europe by the point this car was built, though it still formed the basis of the FIA technical regulations. By 2002, 4WD rally cars in Europe were either WRC cars, or Group N. A WRC Subaru shares basically nothing with a road car. A Group N car is basically standard, but with a Hewland dog box, turbo restrictor, aftermarket ECU, uprated brakes and some other bits (still over £100k new though).
The problem is, a car can still be considered as "Group A", even if it's just got a few extra bits over a Group N one, as fitting certain parts would make it ineligible for Group N. Another problem is that people throw the term "Group A" around because it makes their car sound better.
Putting aside any potential provenance of it being a Possum Bourne car, if it's a standard-ish car, with a factory six-speed DCCD gearbox and a few Group N bits, it might do £15-20k. If it's got a proper gearbox, a catalogue full of Group N bits, or some more tasty upgrades, it could be anything up to £45-50k, but it would have to be a top, top spec car to be worth that. The provenance is pretty meaningless unless the car is in or close to the spec Possum used it, and there is proof that it's the same car.
For reference, this barely got over £20k on eBay, and it's got the Group N Hewland, Ohlins and a forged 2.5 engine:
https://www.ebay.co.uk/itm/Subaru-i...2349624.m46890.l49286&mkrid=710-127635-2958-0
As I say, I'd be wanting to know a
lot more about it before even thinking about it.