I would think the crucial thing to look at - is how the loader actually attaches to the frame - look at the hole in the frame where the lower section of the loader QA bolts on - and compare that against the hole pattern on say a B3200 where that LA504 loader would attach. If the bolt pattern is the same - then you'd likely be able to at least bolt the loader to the tractor frame. You're also going to have to see if the width of the frame on the B2920 and say a B3200 are the same - so everything come out in the correct location.
I have a B3200 - if you need some measurements let me know and I can give you waht you need.
None of this of course addresses the issue of whether or not the frame on the B2920 or the tractor itself - can stand up to the loads of an LA504. But if the frames on the B3200 and your B2920 are similar sized - then I would bet that they can.