My AR4 is Serial No.50,made in June 1993.As far as I'm aware it was one of the last of the steel ones they made.
It has the 17" barrel and I get 80+ shots from a 200 bar fill.
If you can check to see if it has a Ripley reg. or has it been changed, a lot were over the years.
If you do aquire it ,well worth sending it back to Ripley for a service at about £150,might be something to think about when haggling over the purchase price?