I'm assuming that by track truck you mean drag racing. If not you may want to look into the rules concerning modifications allowed for the class you plan to enter and track you want to run at.
There are possible upgrades for both, but they ain't cheap and availability could be an issue.
I'll hit on the rear first since that would be easiest to explain I think. The Explorer 8.8 and most later 9" axles use a big bearing "Torino" bolt pattern, I've also seen it referred to as late model large bearing. Most of your Mustangs (and Rangers) used a small bearing bolt pattern, and that's what most better brake options were offered for. Some companies, like Currie Enterprises, sell a bolt on plate that will allow you to use Mustang Cobra rear brakes on a Torino pattern axle. The Cobra rears are only around a 1/2" larger than the Explorer disks, so any gain would be small for the work and money. That said these brackets will also allow any BBK (big brake kit) for the Cobra rear to be used on the Explorer axle, which could be a big upgrade. I've noticed that Currie also offers BBK to mount directly to the larger bolt pattern axles, but I haven't really looked into it. Probably the best/cheapest thing you can do to upgrade the rear at this point is a good set of pads and rotors. IMO with the explorer disks, you need a lot more on the front before the rear brakes need attention again. Even then I doubt that you would gain much from one of the upgrade options, due to the brake bias of a pickup truck.
The front axle is a bit more difficult to upgrade, and really is the most important since that is where the majority of your braking comes from. The easiest and cheapest upgrade is to swap in steering knuckles, calipers, and rotors from a 95-97 Ranger. Although the rotors are the same size, these trucks have dual piston calipers and a better mounting design. The 95-97 knuckles are also the basis for any other brake upgrade so they are a good place to start, and with good pads and rotors they may be all that you need. If you are interested in more after than then there are two options that are sometimes available, a 12" sport trac rotor upgrade, and a 13" cobra brake upgrade.
The 12" Sport Trac is the cheaper of the two, but at current is also the rarer. This is a bracket that moves the 95-97 caliper out to allow the use of a 12" sport trac rotor. The bracket is made by "gumby" on RPS, but he's not currently making them and who knows when/if he will make more. They do occasionally appear used in the classifieds section though, and a few people have taken his idea and made their own brackets. This upgrade pretty much requires a 16" wheel to fit. IMO this will fill the better braking need for almost any heavily modified Ranger out there, any more than this is mostly for show.
The Cobra upgrade is much more expensive option, but is somewhat more available. It is a hub and bracket that mount to the ranger spindle/knuckle and allow one to run 13" cobra rotors and calipers. Once again it is made by a member of RPS named "TeeRev". He's a professional machinist and had decided to make a few sets when his equipment isn't running other work, as such there is no guaranteed time frame as to when they will be made. I can tell you that their is a waiting list, but at this time I don't think he's expecting money upfront so it's pretty much "put-up or shut-up" when they get ready. When I say more expensive I really mean more expensive. The kit costs $500, but by the time you get it almost another $100 will be added from shipping and import duties (trust me, BTDT). Then you will need to buy cobra calipers w/brackets, and rotors. Best option for that is a kit from one of the many mustang parts sites that includes rotors, calipers and everything else but some misc hardware, about another $600 (Late Model Restoration). You'll also need 17" wheels minimum to run these, so more $$$. This hub and bracket kit should also allow for any of the Mustang Cobra brake upgrade kits to be used, those options also mean more more money spent on brake components and bigger wheels. Personally I don't think any Ranger, no matter how badass its built, will ever need bigger that stock Cobra components. Even the stock Cobra components are more show items than practical upgrades when mounted to a Ranger.
I think your best bet is to start with the 95-97 caliper upgrade, then get good pads and rotors for the front and rear. You would also be surprised at just how much tires can affect braking, pretty much anything to improve the tires grip on the track surface will increase braking potential. Get used to driving with them, then decide if you need better. Gives you a chance to save your pennies while waiting for better to be available. Personally, I doubt that you will need better, but if you did I'd recommend making your own brackets for the 12" rotors.
If your true goal is "stop when i mash the pedal", then none of these upgrades will help you much. I know your 92 does not have 4WABS and I doubt that it has RWABS. With the stock brakes functioning properly if you just "mash the pedal" all you'll manage is to lock them up, and that doesn't help the truck stop any. Doing the same with the upgraded brakes will only lock them faster. The best thing you can do to increase the braking on your truck is learn how to use them. To get them right on the verge of locking up without actually locking, that's where the max stopping power is.
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