Why on God's green earth would you put a 4.3 into a racing vehicle - on purpose?!?!? They're heavy, and they don't really like rpms. I mean, if you had an S-10 that came with one, fine, but, there are so many better GM engines that could be done. As already discussed, Buick 3800 has all the upsides of the 4.3, with none of the downsides - similar power, much better on track, and noticeably lighter. 4.3s are great engines - for a work truck. If you were starting out with a truck that happened to have a 4.3 in it, fine. But for God's sake, don't go through the effort of adding one!
To me, a better choice than both would be the 60 degree V6 family - 2.8/3.1/3.4 or, preferably, 3100/3400/3500/3900. All way, way lighter than a 3800 (much less a 4.3) and a good bit more compact (easier to work on). A lot of 1st gen S-10s came with 2.8/3.1s as their V6 upgrade, so swapping to that from a 2.2 should be fairly straightforward, mounting wise. Do seriously look into the 3900 - lightest of the bunch (much lighter than a 3800), 240hp/240tq. I might can put you in contact with someone who can assist on getting it running with VVT. We started with a 3100 in our Buick, engine did flawlessly, ended up upgrading to a 3500 LX9, because it's just such a damned easy swap in those, and, again, engine did flawlessly. If you're anywhere near NC, I have a lower-mileage, freshly gasketed 3100 (160hp/185tq) that really needs a good home.
Or, you can really go off the deep end, and do a Cadillac 4.9 V8 swap. Uses the standard FWD mounts and the bellhousing bolt pattern from the GM small corporate/'Metric' family, very light for what it is (aluminum block with iron heads - yes, you read that correctly), and they've done well on track so far. Search for 'V8 Miata - the Lemony Way'.
~*BoNuS*~ If you use any of the above engines, the hardware part of your swap should be extremely simple. I'm not positive, but (as I alluded to above), I believe the 2.2 shares similar mounts with all the FWD engines, and I know it shares a bellhousing pattern and starter location, so you can reuse your current transmission. Assuming it's rated to hold enough power, I have no idea what transmission comes in a 4-cyl S-10.
1996 Buick Century - we upgraded our crappy GM sedan with parts from a crappy GM minivan.
"It's got a van motor, a 220 cubic inch plant, it's got van tires, van suspension, van shocks. It's a model with the catalytic converters ripped out so
it'll run good on regular gas. What do you say, is it a racecar or what?" - Blues Brothers, Probably