Looks like a trigger shoe been added, target hammer or ???
I too think you got the best of the deal. My 28-2 shipped October 13, 1975 to Maryland Police Supply. I sold this gun several years ago but enjoyed it while I had it. Mine had the serrated service trigger (.265") and the standard semi-target hammer (.400").
The Op's gun appears to have a trigger shoe and I can't tell if it has a wide spur hammer bigger than the .400" semi-target.
I'm posting an add for the gun when they were new. So....$90 in 1972 to approx. $750 (your 36 + $150) in late 2024 ??? Yea...I'd say you got a terrific deal.