There's supposed to be a horseshoe-shaped bracket the air cleaner, right about where that hole is, where the bracket on the MAP sensor would just slide down into, and sit there on the side. Looks like that's all messed-up and they're using a chunk of electrical wire to hold up the sensor. I'd plug that hole.
You could relocate the MAP sensor to the firewall, it's commonly done and would look cleaner. Just make a bracket or heck you could even zip-tie it, and it'd look better than it does now! The MAP is pretty much self-contained and won't be affected by how it's mounted. It just needs the vacuum line and electrical connection and it's good to go.
Take a look at the driver's side of the block. If it's truly a 3.4, it'll have some "X" reinforcement castings on the block, also there will be a big "F" that you can't miss. I'd imagine that stands for "F-Body".
The plugged-off vacuum line could be for the EGR, does it have an EGR valve and if so, is it connected?
If the other end of that plugged-off line goes to the TBI, maybe it's actually the hose that goes to the EGR control solenoid. Does it have one of those? I couldn't make it out in the pics.
Someone here should have a vacuum diagram for a 2.8 TBI, it'll be the same hookup for a 2.8 TBI system bolted onto a 3.4.
BTW if you have small exhaust (1-7/8"), you'll get an amazing increase in power by improving that. Go to 2-1/4" back of the cat, with a turbo muffler.
Another big improvement for the 3.4 swap is to bolt on a TBI meant for a 4.3 90-degree V6. This TBI happens to have 1-11/16" throats, which is the perfect upgrade size for a 2.8. You do have to pull the intake manifold and take it to a machine shop to have the twin TBI intake holes bored out to 1-11/16". If you don't, the larger-diameter throttle blades of the 4.3 TBI will hit the smaller holes. And no sense having a big TBI if it's going thru 2 little "wheezy" holes, eh?
Those 2 mods give an incredible increase in 3.4 performance. I have a '90 Trooper with the Camaro 3.4, and for the longest time I ran the stock exhaust. When I finally did the mod, it was like having a new engine in there. Couldn't believe the power. Already had the big TBI (a Holley Big-Bore, which is NLA). But even with the Holley, it needed a better exhaust and I was very pleased. Still runs great after doing the swap over 21 years ago.
This is a good page to read for performance tips for any Iron-head 60-deg V6, if and when you're ready to do things to it:
Anyway, enjoy your "new" rig, a much lighter S10 should be really fun to drive with a 3.4 in it!