Fazakerley made No4 Mk1s into the PF89xxx number range - actually yours is one of the highest numbers seen for a Mk1. There was a big overlap in the numbering with Mk2s - I have PF 59871, which is a Mk2.

Most of the PF Mk1s and early Mk2s into the PF2xx,xxx range seem to have gone to South Africa.

Many South African rifles seem to be centre-bedded or "loose bedded" (ie barrel just lies in the barrel channel without any bedding pressure). As many of the rifles currently coming out of South Africa have warped forends, I wonder if Fazakerley was knocking out rifles with poorly-seasoned wood?