Location? There are several teams running S-10s, you might be near enough to one that they'd consider coming to give you a hand, spare parts, etc. Take advantage of people who are willing to come take a look at your pile of crap - they can offer really, really good advice that can save you a lot of headache come race weekend.
Extended cab or regular? I don't think it makes a huge difference, but, extended cab is a lot easier to work with due to the extra space.
I think those were using the 2.2 by then, not the 2.5 Iron Duke, correct? Does yours have the oil cooler plumbed into the radiator? I know a lot of 4.3s (at least on Blazers) did, not sure about the 4-cylinders.
I'd strongly consider upgrading your radiator - I don't think those engines are particularly bad for head gaskets, but, I'd also imagine the factory cooling capacity is marginal at best. I don't remember offhand what other random GM stuff will fit there, but, if I were you and the money for a new radiator wasn't in the budget, I'd take measurements of the engine bay to determine what size radiator could fit, and wander the yard to find one that's a lot thicker that will mount into that spot (GM or not). A junkyard radiator isn't Choice #1, but, neither is what very well may be a 5/8" thick radiator on an old truck. I'd avoid the tank-mounted oil and transmission fluid coolers, if possible - they rob radiator capacity, and a separate oil cooler is generally preferred (although, you'll find that your easiest radiator upgrade route will probably have the in-tank coolers. If so, no big deal, just not 'ideal'). Have a look at the junkyard, you might get lucky - I bought a perfectly fine radiator for my Blazer for $30 last summer. In the Buick, we've got a radiator that we found in a '91 Oldsmobile Silhouette minivan with over 300k miles on the odometer, that had trees growing up through the body - radiator looked like it had been in there about 5k miles (it probably was replaced to try and fix an overheating issue, which turned out to be an intake manifold gasket which, while not really that big of a deal, can easily be the last straw on a basically worthless vehicle.)
Oil cooler - a great idea. If your truck already has the factory oil cooler lines to the radiator, take them out of the radiator, and put them into a big dedicated cooler mounted to the front of the radiator (or somewhere that gets a lot of airflow). You can get a really good plate cooler from a yard for $10-$15 - check larger vehicles, they tend to have really beefy dedicated transmission fluid coolers. Alternatively, if you don't have factory oil cooler lines, an oil cooler sandwich plate adapter with lines to a cooler should be fine, and not too expensive. If you just absolutely don't want to change the radiator, this will go a long, long ways towards helping keep the engine cool. I'd do both, but, I understand having a list of priorities.
Also, curious about the electric fan you put on - is it pulling air through most of the radiator? I only ask because, I've seen some really, really pitiful fans on cars before. Strong factory fans are pretty easy to come by cheap, no reason to use something crappy.
Driver comfort - if your heat tolerance is low, consider looking through some of the things people have rigged up to keep themselves cool in the car. A cool suit is really nice, but, something as simple as a way to get water or fresh air while you're driving can make a big difference on those hot summer laps. I mean, I haven't done it on my car, but, I hear it's a really good idea...
Lastly, add information! I have no idea what the gauge setup is on a '95 S-10, but, I'm guessing it leaves a little to be desired. I don't know that you'll be able to pull all that much information from the computer, but, a real coolant temperature gauge, an oil pressure gauge, and a voltmeter would be really good to have. Oil temperature if you can get it. I'm forgetting one, but oh well (maybe it's transmission fluid temperature, which you won't need). A shift light is not a bad idea - that is most certainly NOT an engine that likes to rev, so you'll want to make visits to 5k rpm a rare occasion. I know, I'm sure you wanna race, but, upshifting early will help the truck stay out on track all weekend. Don't get in the habit of winding it all the way out in every gear right off the bat, unless you're okay with stuff starting to blow up.
I like to make a search of the local parts stores and junkyards near the race for parts that we might need - wheel bearings, ignition coils/modules, random sensors, etc. If there's something the car isn't really known to be iffy about, but is known to be a problem in racing in general, but I can get it from the local parts store if I have to, I don't worry so much about lugging a spare around.
That got a lot longer than I intended. Hope some of it is useful!
1996 Buick Century - we upgraded our crappy GM sedan with parts from a crappy GM minivan.
"In a race where everyone runs a Buick V6, their Buick ran a Chevy V6. And a crappy one at that!"
IOE - Lemons Block Party (minus the block party) CMP 2020