If I remember correctly on the front the distance between the air bag mounting plates is between 8 1/4" and 8 1/2". If this don't make scence feel free to P/M me.
With it being a 40' does it have 2 axles or is it one of the 40' with a tag?
With it being a 40' does it have the C-12 Cat engine? (can't recall if they used them in 96') If so you need to go over to the Cat engine club CAT RV Club
and get signed up. If you are a member you get a 10% discount on Cat parts. Every bit helps.