I'm considering a lever action converted to 50/2.3 -- that is, a straight-walled 50-110 shortened .100 inch (a 50 Alaskan with 2.3 inch case rather than 2.1). Cartridge overall length would be 2.70 inches. What off-the-shelf dies will reload the cartridge acceptably? Would 50 Alaskan dies reload such a case better than 50-110 dies? Or if neither is acceptable, who can make the correct dies?

I would suggest 50-110, especially if you are going to shoot it in a lever gun. full lenght sizing is key.

O.K. This is supposed to be a "family" on one case... So, theoretically, any .50/?? should do an o.k. job on resizing. Obviously, seating with a die set longer than the intended case, problems. So cut some off a .50/110 die? It has been done, bet.

Regardless, anyone making the dies, depending on hospitallity, should be able to make dies to suit. RCBS custom shop/ huntingtons.com makes a business of this. ch4D.com is another. LEE does a bit of this but haven't looked for this biggie. Hornady might. It can be done, just costs. Actually any machine shop could. But with the learning curve, big costs. luck.

Actually, I have seen Lyman 50-110 dies available as a "cowboy" set relatively inexpensively.
I can see your point about a seating die that is too long. It is vaild! My guess is that there may be enough adjustment for .2 as bullet lengths vary so widely in 50 cal from a 300 grain to 500+ grain.

You might try 50 alaskan dies, they should work just fine for you.

45/70 dies will load 45/90 rounds same differance .300 ! so as Doug advises 50 alaskan will do the job for your round that is .100 shorter than the 45/90 or 50/110 .