I looked at this problem for other early type bikes that use the Generators. It IS solvable.
NEWS FLASH: Alton does NOT make all their components, they adapted parts from other applications.
So can you.
I started looking at other designs, And there are a few that are similar in size and shape of the E3L alternator/generators, and thats what Alton did is adapt one of those in a cylindrical body similar to the E3L,
Look at tractors, lawn mowers, ATVs and some motorcycles. (There are catalogs for armatures that manufacturers use is a good place to start). The biggest problem I found was heat. A typical auto type alternator tends to be short and larger diameter along with alloy body and lots of venting. In a cars engine compartment there is also airflow,, not a lot, but enough. If you seal up the armature in a solid body you have to dissipate heat somehow. (I believe thats what kills most ALTON units, they do fail sometimes)
The second problem is drag, In high loads the tooth load for a gear driven unit can be quite high and I was told early ALTONs had some teeth shredding issues on Triumphs. (Resolved with better materials. I have always felt that off the crankshaft is superior to off the timing gears. So did Triumph-BSA-Norton in later designs whether it was a rotor/stator or, as Velocette or Indian did with a belt.
The problem is adapting and room. Early EVO sportsters (1986 and up) ran a stator assy on the backside of the clutch basket, there was some issues of them failing, later models moved them to the crank position. To adapt one to a A7/A10 crank you have the crude cush in place, If you could move the cush elsewhere such as later BSA-Norton-Triumph did it is possible to install a skinny asian made rotor/stator. Or, if a belt drive is installed you could run a pulley up to a external alternator body.
Or,, do your research and make your own version of the Alton. I was in the midst of this in the 1990s when the early versions of the ALTON came out, looking at such a limited market I concluded wholesale manufacturing and production with an existing product was not worthwhile/viable.
I still believe a superior product could be made from a quality and price standpoint.
** There is MANY ways to engineer something, just consider some Asian 2 stroke enduros use a stator for charging and ignition, But thru eeelecktrikal trickery,, it also can be a starter. (See Yamaha DT1), I dont think it could ever work on a A10, but it IS an interesting and clever design.