Well for today the drive shaft has now been shortened 3 1/2". And I drilled the new holes to move the cross member back. You have to move the cross member back and you can still use the original mount and cross member but have to make a plate to adapt the mount to the trans. That will happen after the trans is in the truck. This moving the cross member moves it back about 6". Here is a picture of my test fit to give you an idea.

You have to drill three holes two in the lower frame rail and one in the upper. You can't see the upper one in the picture but it is a pain to drill and get the bolt in because the cab is setting so close to the frame. Elongate that back top hole so you can get the bolt in from the top, or use a really short bolt so it doesn't hit the floor pan coming up from the bottom. I chose the elongate method with a bolt from the top side. You can see in the picture the original top front bolt, I couldn't get it out because of the cab being so close to the frame. I just put a nut on it and tightened it up in place so it doesn't rattle around. Well thats about it for today.
As to the horse power limits of the Ultra Bell I really don't know either. You could call JW Performance and ask them. They were really nice and helpful when I called them. I am sure they could answer that question.
Enjoy