Just looked in my old Minifigs catalogue (circa 1983) for the PB177 code. There are no PB codes beyond 84. Interestingly there is no PB17 code either! I used to pass the shop door daily in the late 70s and went in too often for my wallet's good. Maybe you could post a photo!
IIRC, Minifigs 25mm fit in very well with Ral Partha and RAFM, size-wise. Essex '25mm's' were noticably larger. Probably had some Irregular figures, don't remember much about them... Sic transit gloria...
Thanks again for all the information. I think they're the spearmen Ax(O) from II/2 in the DBMM lists 'Men armed with short spear and round shields coming from this general area are depicted as tribute bearers at Persepolis'.
I can't find my 'Armies and Enemies of the Greek and Persian War' at present to look them up.