Is it an '86 or '96? Grill is telling me '86, I have an '83 single cab I've been kicking around the idea of building or just selling. Either way it's a cool rig. Really that thing is a beast as it is and doesn't need much done to get out and explore forest roads. I would prioritize making sure the motor and drivetrain are in good order before worrying about a solid axle swap, the TTB will ride better than a solid axle anyway. Like mentioned above some more info on how you plan to use it would help with ideas, but really you can use it as is with not many mods and that will tell you what you should do with it. Below I'll list off what I would do to it, then use it for the summer making notes of your wants and needs to work on over the winter.
-Basic maintenance and mechanical needs addressed
-Basic recovery gear and knowledge of how to use it
-Solid recovery points front and rear
-Tool kit with any vehicle specific tools you figured out you needed while doing the above work
-Matching full size spare, quality jack and tools to change the tire
-tire plug kit and quick repair valve stems
-Tablet and tablet mount in the cab for navigation
-additional USB or 12V outlets in the cab for charging
-Some decent weather proof rubber maid type boxes for gear
Optional Items
-Rear locker
-Off Road lights on Bumper
-Harbor Freight knock off Jackery
-Some type of awning or home brew tarp setup
In my experience the best way to figure out how to build your rig is get out and use it before putting in all the time and money. You could do all the stuff above the optional items, save yourself a bunch of money by not doing all the "overland" mods and use it all summer. Then after a season of using it you'll know where the improvements are needed and where best to spend your time and money.