Don't jump on the check book just yet... Let me try and answer some of the Q's you have and offer a little opinion.
"runs like crap"...why? All FSJs from about 1980 suffer from a horrendous case of retarded emmissions overkill. They also use some of the worst carbs and the ignition system has much room for improvement! Start with deciding what is the cause before you jump into the need a new engine realm.
Waggys are a tiny bit more work to clear tires due to the rear set of doors coming closer to the wheel well opening. That said, I run a set of 33x10/50-15 BFG MTs on a 4" Rustys spring lift. Steering was an easy fix with a drop pitman arm. You can get the same set up on yours as long as you stick to narrow tires and you may have to trim a tiny fuzz at the openings. Fitting 35s is more work. A lot more kinda...But it can be done several ways....
BJs, Rustys, and I think one other place sells a 6" spring lift and you may or may not get away with the DPA for steering.?. You could do a 4" kit and a 3" body lift but most folks have shunned the old school block raisers...Your preference...
The other way is going to net you the best ride, flex, and lift. And its even cheaper initially...ish. Go SOA and flip the rear shackles. BJs sells Tads kit to do this. But it Will require something more than a DPA to fix the steering. Promise.
As to the axles...You could run 37s on what you got if you wanted to...The rear AMC (not a DANA) model 20 is a much different animal than what is found in its little CJ brothers. The Center sections are the same but the tubes out are all much beefier! And unlike the grenade prone CJ versions...the FSJ 20 has 1 piece axles from the factory. There is no more to really do other than add lockers and certainly REGEAR! They will likely be spinning 2.72 ratio...great if your trying to set a land speed record! Worthless off road...and a true dog once you step up tire sizes.
Final word of advice lest I sound "preachy"..Wander over to the IFSJA site
http://www.ifsja.org/forums/vb/
everything you have, will, or shouldn't want to know is there...as am I. LOL!
Good luck and welcome to the fold!
I just picked up this 1983 Brougham with a 360. The body has NO rust...advantage of living in a desert... abut it runns like crap.. and it has a D20 Rear axle! So, I was wanting to set this thing up for Overland, but I am not sure if I want to invest everything into it if it will not suit my needs. First, may need a new motor, $2700 with 100k warantee. and I am thinking 6 inches of lift for 35s or 4 inches for 33s. I dont trust the D20 with big tires, but have read a lot about strengthening them. May look at D60 swap or D44.
I had a TJ built to the hilt that would climb a wall, but this is for overland travel where I imagine I will need a vehicle that can handle hundreds of miles of sand, and Level 3.0 trails.
So my first questions are:
1:What size lift do I need to run 33s and what size for 35s?
2: Has anyone run the D44 front and D20 rear with big tires with success?
3: How about the Select track T-case? Will it hold up?
4: How about the design of the steering? Do I NEED crossover?
Any help you can offer would be appreciated. I am trying to see if the cost will be worth it or to scrap this rig and start with a different platform.