Ouch. Yes there is a 5 speed that will mate to the SOHC, good luck locating one.
I recently converted my 88 BII from a 5 speed to an automatic (opposite of what you want) and it was a LOT of work. You should know I do this kind of stuff all the time, this is not the first truck we have done, and I gathered parts and did research for over 6 months. The actual conversion was done in one weekend, however I spent the next 3 months working out the bugs. No matter how much planning you do you will run into snags.
You would be better off buying a 5 speed truck. The Sport Track was available with a 5 speed and the SOHC.
Basically unless you are a skilled mechanic, have a ton of resources (junk yards, books, friends) and are used to doing this kind of stuff, dont do it.
You will have to swap out your computer and make some wiring changes. You will have to remove the shift linkage you have now (cable operated column shift) You will have to locate and install the brake and clutch pedal assembly for your truck (no easy task). You will have to install a clutch master cylinder, resevoir, and hydraulic lines. You will have to get the Flywheel from a 5 speed SOHC truck, clutch, slave cylinder. You will have to cut a hole in your floor and carpet, install the shift boot and everything associated with it. You will have to remove your auto tranny cooler and lines, plug up the holes in your radiator, or swap radiators, You will have to remove some wiring from your computer harness (unless you like sloppy work).
That is just the tip of the iceburg. You may also run into exhaust clearance problems, you will need the 5 speed starter, you will have to remove the kick down cable from your truck, etc.....It gets messy, especially with the later model trucks such as yours.
Of course now anything can be done, it;s just a matter of time and $$$$$$, hell I;ve seen a Wrangler with a Viper V10 in it, so it can be done.....it's just a matter of how far you are willing to take it, how much $$$$ you have, and how much patience you have.........
Now keep in mind my truck is an 88 BII with a complete Explorer drivetrain. The auto tranny came from a 94 Explorer. The floor shifter, bell crank assembly, and tranny shift linkage came from an 84 BII, the clutch brake pedal and clutch block off plate came from an 86 Ranger, the kickdown cable came from an 88 BII, the starter came from a 94 Explorer, the kick down cable bracket came from a 87 BII, and there was a ton of other stuff involved. I built the wiring harness myself and swapped out to an autmatic computer for the tranny. The flexplate, hardware and torque convertor also came from a 94 Explorer, the vacuum line came from a 94 Explorer as well. Now keep in mind we had the know how and access to the needed parts to do mine, we had done this before, and we basically know everything there is to know about Ranger/BII/Explorer drivetrains from spending years building them up and customizing them. I spent countless hours and trips to junk yards collecting the parts, I completely removed the wiring harness from my truck (easy for me since I built it and installed it 3 times) and modified it for the automatic. And I still spent 3 moths trying to get it right after the initial conversion was done. The biggest snag I ran into was my JBA headers had an 02 sensor running right into the shift linkage for the 84 BII, I took it to an exhaust shop to have this fixed and they ended up frying my entire electrical system (computer).
So I just want to let you know what kind of project you are thnking about tackling. I would never have attempted this without the help of my friends and if my truck wasnt so old. This conversion would be 10x's harder on a 98 truck, the entire steering column would have to be swapped out because there is no such thing as a floor shifter for a 98 Explorer. You see Ford actually made parts to put an A4LD in a BII, so it was just a matter of making all the Ford parts work together.....
In either case research is the only way to tackle something like this. TONS of research........You need to know every single thing there is to know about how the clutch, tranny, starter, wiring, etc work before you even start...........Oh and look to spend a minimum of about $8000 on your conversion, if you can find a 5 speed and do all the work yourself............
