You have to make the final decisions yourself. All I can give you is what I would do.
Having owned an '86 IROC-Z Camaro in the recent past, I can tell you that I love the torque response of the tuned port injection. The 305 needed it since that engine was such a dog. But bolt a tuned port on a 350 and you've got all kinds of torque. On the same 350, I previously had it in a Corvette with a Wieand Action Plus intake and a Holley 650 double pumper carb. When I bolted on the tuned port EFI, I'd say I easily picked up at least 50 lb-ft of torque everywhere in the rpm-band. The only thing I lost was the upper 300 rpm that I used to get with the carb. But with all that torque, I never missed it. The TPI has a reputation for running out of breath at about 4400 rpm, but I can tell you that it is more the RV-type stock cam that was to blame for that than the design of the TPI. I had an Iskendarian 270-Megacam in that engine, and with the tuned port bolted on, I easily made power to 5000 rpm, and I'd say it ran out of breath at about 5200 rpm. But it had torque enough to roast the tires for a full city block.
Why did I get rid of the '86 Iroc? I didn't want to tackle all the electronic gremlins. Mirrors that didn't work, door switches that quit working, broken wires in the engine bay from 21 years of baking in the heat and getting brittle, 21-year old fuel injectors that were all failing...I could have restored the IROC, but frankly, I didn't want to spend over a grand chasing all the electronic gremlins.
So based on that, $200 is a great price for a TPI Trans Am, but I would use it for a parts donor. Mostly because of the electronic gremlins in a car that old, and partly because the 305 will never be a good performance motor. You should pull off the tuned port, complete, manifold up to throttlebody, including the MAF sensor in front of the throttlebody. You could check the rear end ratio. But I could tell you what it is, depending on the options. If it is a manual transmission, then 3.23 was the standard rear end, with a 3.73 optional. If it's the auto tranny, then the ratio is a doggy 2.73. I'd say if the tranny works well, why not grab it, provided it's a stick shift. If it's the automatic, forget it. The 10-bolt used in 1986 uses a cone-type posi, which works very well until it wears out, and is considered non-rebuildable. You buy a new one. The year 2000 rear end is a perfectly good unit also, and is newer, and should also have disc brakes. It also has 14 years less wear on it. So I'd go with the 2000 diff unless the '86 diff is a 3.73. And if so, that would tempt me.
Or keep both diffs, one as a back-up.
I wouldn't try to reuse the stock wiring harness, but DO pull the computer and keep it. The stock harness will only save you $400 bucks over a brand new Painless harness, but like I said, it has been baked for 22 years and is brittle. It is worth $400 bucks to get a new harness. You can reuse the fuel injectors if they are in good shape. If they aren't, then buy a new set of those from Summit Racing.
Don't be afraid to cam up your 350. Just like any engine, the tuned port responds well to a slightly bumpy, rumbling cam upgrade.
And if you don't want to spend the cash now, then box up the TPI and run the carb for now, like I'm doing on my '52 GMC. Nothing wrong with that. But I WAS getting 22 mpg on a powerful '86 Iroc with that TPI. Something to think about.
