I had them on my 05 Road Glide so will go back even later than that. Maybe 97???? Very nice pipes and if in good shape a fair price IMO. I just bought Akrapovic 2 into 1 for my Road King and their site says 06 and later. No reason it won't fit my 01.
The only reason they don't show to fit 99 to 06 is oxygen sensor holes. Those can be plugged. I run a Thundermax so I needed O2 bungs anyway and they bolt up perfect. As far as I know anything older than 99 was Evo not twin cam so that won't work. Anything newer than 08 is the new frame so I'm not sure there