That may well be the solution. The Keppeler literature specifically states that no alteration of the choke is necessary, but also that the insert has to be individually fitted to the host gun and proofed. So the fact that it will clear the less tightly choked right barrel of your drilling may make that the better candidate — with the added advantage of being able to use the set trigger.
Interesting little detail: Keppeler listed the 6x70R for 12, 16 and even 20 gauge, whereas the larger insert calibers were specifically marked “for over-under guns only.”
