A peep sight might help a lot, like a Foolproof.
As the eyes age, it becomes very difficult to see the target, the front sight and the rear open sight. With a peep, only the front sight has to be seen.
But a 3X scope would be better.
Get him a 94AE in 356 or 307. The Angle Eject is similar to his rifle, but ejects to the side so a low scope can be fitted.
I have a Marlin 336 in 35 Rem with a scope on top. Something like that would work, too.
I note that the EE Forum here has a Win 94 in 307 and another guy has a marlin in 32 Spl.