don't think they offered the 20ga with a 28in barrel until sometime after 2000.....
I bought one new, from GSI (the importer), back in 1993. My memory told me it had 28" barrels, but my records say 27", which seems odd.
I remember patterning 20ga pheasant loads in that gun. Never shot any 3" shells through it, but I did try some "short mags" with 1 1/8 oz shot. They'll get your attention in that gun!
Agree that there are certainly Parker Repro 20's out there in that price range. You'll have to look a little to find one with double triggers, but they made more 20's than any other gauge, so you shouldn't have too much trouble. The Repro might be a few ounces heavier than the Merkel.