I'm doing this from memory, which isn't what it used to be, so bear with me. I think I'm accurate but if not, better minds than mine will join in.
The letters and numbers have meaning. Mine is a 2004 E7. E means they went from 4 speed to 5, 7 is the years after making the change. They went from 4 speed (D series) to 5 speed in 1998, I believe, so a 1998 would be an E1. '99 would be E2, '00 would be E3, 01 an E4, 02 an E5, '03 an E6, and so on. I believe the letter changed to N with fuel injection. 2004 was the last year you could buy a 1500 with a carb, if I recall correctly.
If you have a 1500A thru C, I believe they were the old style Vtwins called BUBFs. They were made from 1988 to 1997, had two carbs and two air cleaners mounted near the front of the tank underneath it, a plain billet motor, a split L/R exhaust that came together on the right side behind the motor, and a 4 sp gear box.
1997 midway through the year they changed the design and introduced the more modern looking single-carb 1500 but it still had a 4 speed gear box.
04 1500 Classic
Sissy bar, luggage rack,
light bar, 2" risers,
Isogrips, Fatbar crashbars,
offset hiway pegs, tank bib,
new brake pedal, throttle lock,
Cobra Lowboy Shotgun pipes,
Baron's Big Air relocated right side,
tombstone tail light,forkbag,
detachable hard leather bags,
alarm, power port, clock,
and a cool cupholder