Besides the clear choice, what other years and models could I get away with for a solo seat?

 

Not understanding your question . Try and explain more you will get help .

 

If it's a stock Harley saddle, '04-'06 will fit. If its an aftermarket saddle from Harley, some will fit, some won't. It depends on when it was manufactured. If it's another brand of used, aftermaket saddle, you'll want the fitment specs from the manufacturer and the ability to return it in case the original owner screwed up.
If you don't mind re-locating your ICM from under the seat (or lowering it in the frame), any seat from any Sportster '04 and up will fit. A saddle from a 3.3 gallon gas tank bike will be longer than a saddle from a 4.5 gallon tank. A 4.5 seat will go onto a 3.3 bike, but there will be about a one inch gap between the nose of the seat and the gas tank. Some people prefer this look, feeling it's more chopper-like. A 3.3 seat will need to have its nose re-shaped in order to fit on a 4.5 bike (remove seat cover, trim the foam then staple the cover back).
The ICM/ECM is in different locations for '04-'06, '07-'09 and '10 up. '04 to '06 it's under the rider's butt. '07-'09 it's sorta under the passenger seat. '10 up it's not under the saddle at all. Different seats make allowances with a pocket formed into the seat pan that allows the seat to fit over the ICM/ECM. Some seats, Harley and other brands' aftermarket, have a design that permits both ICM/ECM locations, but that's where it depends on the year it was manufactured. No factory, stock seat, any year, permits both locations. The stock seats are dedicated to the module location it was designed for.
The numbers molded into the plastic seat pan of a stock Harley saddle don't tell you anything. It's not a part #, and it's nearly imposible too tell what it fits from that # alone.
In a large nut shell, that's it. If you have a used, stock seat in mind, get pics of the underside (seat pan), and I can most likely tell you what it fits.
There are ways to hack a two-up saddle to make it a solo.

 

Thanks NY, SCUBA answered it. Thanks for your help.