Wackypedia implies there was one mortar carried based on the M3 chassis, and two similar ones on the M2 chassis (one mortar firing forwards, one firing backwards). Guessing the BF ones are the M3 so should be fine.
Also can't see many people noticing, or being that bothered.
of course people will quite rightly be totally triggered by a model weathered with sandy dust being used in north west Europe...
I'd run with it, I don't think there was ever a different model made by BF when these things were in metal/resin