BTW, what "9.5 inch" axle are you trying to use? You do realize that there are no 9.5 inch diff front Cruiser axles that are as wide as the '80 axles, yes? And that the low pinion 9.5 inch diff will not fit with the'80 series steering linkages. And that the '80 birfields are stronger than the smaller ones of the earlier Cruiser axles? And that the brakes are superior?
I really am not sure why you are trying to reinvent the wheel and thinking that you will save a single penny in doing so. You will not.
You have a 3FE under the hood. You really do not want anything larger than 35 inch tires unless you are going to regear and/or hotrod the motor (and there is not a lot of "hotrod" that most can do to this engine). Even that will be pushing it if you are really gonna play in the mud. You can put together a 3 inch lift for lunch money by watching for used stuff that is always floating around and put some 35 inch tires on it and go play.
I see hacked up FJ80s too often. Guys get them cheap and figure "why not". I bite my tongue when these guys want to brag about them and show them off. I avoid thinly veiled suggestions to "go wheeling sometime" because I don't want to have to deal with getting them off the trail when the break. I am offered "screaming deals" fairly often too. I usually pass on them even as parts cars.
An '80 is not an 1990 S10 blazer or Ford Ranger pickup or Jeep Cherokee. It is not a rolling POS where ANYTHING you do to it is an improvement. Don't go into owning one with that outlook.
Am I correct in my impression (from your profile and keyboard style) that you are 18? If so, no offense intended, but if you are 18, you simply have not had time in life yet to gain a lot of fabricating experience. No matter how smart you are or what you aptitude is, it takes experience to create skill. And knowledge. You are gonna want that before undertaking the sort of modifications you keep talking about here. Along with that, I have to assume that you do not have a lot of hours behind the wheel of an '80, on or off road, to learn just what they can and can not do at various levels of modification.
We've all been there. (I still remember my attempt to install full elliptical springs under the front of an FJ55! That abortion never got past the "cut the frame up and weld s*** on" stage before I started to see the flaws in my plan LOL)
Start small. Learn what your rig can do stock and mildly modified before you hack it to pieces with poorly considered modifications.
Mark...