Congrats...dont see 1928ac's for sale very often
do you believe the finish to be original? (i notice the rivets on the rear sight are not silver)...the type of sight is most likely correct for your year
i prefer the police guns as they are often matching # and original finish....
cant tell from your pics...who is the maker of your drum? (united industries?)
It looks like the original finish to me, but I'm not sure. I've told the story before of me sending my 6" Colt Python to the Colt Custom Gun Shop to be refinished about 20 or 25 years or so ago, and to this day I can't tell it's been refinished. Someone more capable than me needs to look at it and answer that question. The pictures, however, don't really do it justice. I used my three year old Motorola phone in not the best light conditions. I probably need to get my Canon camera out and take some high quality pictures. It's a beautiful gun IMO.
The "L" drum is a United Specialties drum which I bought while waiting for the transfer. I researched it in The Ultimate Thompson and, if I recall correctly, it's a 4th generation model.