My wife has a 2006 883L that I just put a 4.5 gallon tank on. I'm the process of sourcing a new seat for her. She like the look of the Roadster seat but the only year to my knowledge that it came with a 4.5 gallon tank was 2008 (and maybe later, I dunno if the model was continued). Those bike were FI and the ECM stuck up pretty high so my guess is the seat pan is different than the 04-06 carbed seat pans.

So the question is: If I find a 2008 Roadster seat: will it fit???

 

If you re-locate your gal's ICM, which is under the rider's butt in the factory location, any seat from 2004-up will fit. The '04-'06 saddles have a pocket that accommodates the ICM (under the rider's butt). On '07-'09 Sportsters, the ECM is located in the rear fender. Those seats have the pocket in the seat pan positioned accordingly. The seats aren't bolt-on interchangeable from either direction. However, if you relocate the ICM on '04-'06 models, an '07 and up (including 2010 and up) will fit. I've heard stories about people placing them next to the battery or lowering the ICM in the frame, but I've never tried it. Saddles from 2010 and up don't need to have provisions for an ICM or an ECM because the bikes' design moved the ECM out from under the saddle to a spot by the battery.
Here's an example of the ICM relocated to the battery compartment using zip-ties (not my bike).


Edit: A seat for the 3.3 tank will fit if you peel back the cover where the saddle meets the tank, trim the seat foam with an electric carving knife (like you use at Thanksgiving on a Turkey) then re-attach the seat cover.

 

This response is exactly why I come here. Thank you friend, you've given me options. All I need to do now is choose the seat carefully so I don't wind having to stop every 120 miles because her butt hurts;-) If get the the right one, its only one fuel stop to Deal's Gap.