Your both right re the mod
The Disco is 100 inch, so if you start with a 109 tub you can chop it down to a 100 inch, or chop the chassis by 18 inches (or maybe 19) and then use it for a hybrid 90/88.
I musty admit though, that my advice is taken from "armchair experience" via TV and Google
Id watch a 4x4 is born as its just great watching, and it was on discovery turbo all day today. (but iv seen it 3 times now so resisted the temptation)