Since that's a FAT with the chainstay U-Brake / Roller cam brake mounts, it is likely from 1988 or 1989 (best guess). If that is the original color, it would have been a custom Imron paint (likely painted over a stock black epoxy powder coat, which was the norm then)
Give us the serial number. I can't say for sure if I welded the entire frame or just did the bridge tubes, pizootie tab, seat tab, brake mounts and rear dropouts. That was considered finish welding operation and the main triangle welding was first welding operation. I did almost all of the finish welding operations back then (mostly because we only had one rear brake mount fixture) When I started in November 1986, I worked part time during the day and then went to my second shift welding job at the tantalum factory. We had another guy named Bill who worked at MIT during the day and he would come in part time during the evening. We usually had a few minutes of overlap. He welded a lot of the FAT main triangles and I welded most of the Wickeds and did all of the finish work. Chris Igleheart built a lot of the forks and would tack weld frames in the frame jig.
In June 1987, I quit my job at the tantalum factory and came on full time. Bill got into a vending machine business and that became his side hustle. Sorry, I can't remember his last name. When he first came on, we were setting up his welding machine and discovered that there was no ground lead or clamp for it. Helfrich just happened to be there and just said "Grounds are for fags!" I know its not politically correct anymore but we laughed and Bill wrote it on the wall. It was probably still there when the building was demolished.
Good luck with it
Scott