Paul, I have just checked for the position of the chassis ID plate on one of my BF 3023s. It's a small plate, perhaps 3 inches square, riveted to the panel below the windscreen to the RH side of the dash mounting panel and quite visible, even from the driving position.
The other van is a bit more difficult to get at, especially after dark at this time of year but I may see if that one is the same in due course.
The van I have just checked is a BF 3023, 1960 and the chassis code starts 98A. Yours may be similar or may be on the updated chassis code system which would actually give BF3023 as the chassis number prefix.
As far as I can establish, all 25 cwt and 30 cwt models had the longer wheelbase (10' 3"), either Mk IV or Mk V. Mk V 'long' (123") could be either BF2523 (1956 on) or BF3023 (1957 on), both running to 1966, and the shorter wheelbase was used for the 1 ton Mk V (1959 on) with designation BF2011 (20 cwt, 111" wheelbase).
Hugh