Lovely when the archive can be searched and you get a result.

It is recorded as being despatched to a Mr E. AYLING in February 1989 as a 7.62 Model 1200 rifle.
He also had J1050 both written down as TEST ACTION what ever that may mean your end. Highly probably used to sample his particular shooting prowess at the time.
Is he still alive? and is it still 7.62?
Interesting, because I too would have said it was an M84, because others were produced in August 1990 with the J suffix too and marked down PH M84 BISLEY.
Hope that helps in someway.

Entry 858 PARKER HALE ARCHIVE
Gil