Disastrous and overly severe!
I couldn't agree more. Rascal, you really don't know much about the mechanics of western bits and you've been looking in all the wrong places if you can't find a nice mild one.
Taking a horse that has been ridden for most of his life in a snaffle or a kimberwicke and putting him in a bit with 8 inch shanks and a solid mouth is an accident waiting to happen. Everything about that bit is brand new to him and, IMHO, it is overly severe for a horse just coming up from a very mild type bit. I won't even ride my old broke horses in bits with 8" shanks because I feel they are just too much for what I need.
If they will let you ride in a snaffle, then that's probably what you should do.