Exactly the reason to give that used endurance saddle a try, it might work great for you.
Oh, I dunno. I have always ridden equal time in both western and english (both from a H-J and Dressage background), and I remember no problem at all with my Fallis Carmichael Roper saddle as to stirrup balance underneath me. The seat was narrow enough for me also.
The wade saddle I am riding actually does give the twist and balance of a good dressage saddle. It's the only western saddle I've ever ridden that does- I think that for some people's pelvis/conformation, finding a western saddle that rides like a dressage saddle will be like finding a needle in a haystack.
There is really no good way you can, on any kind of western tree, get the twist and balance you have in an English saddle.
Wade saddles were also said to fit closer to an English saddle.