Yes, you will need a thrust plate or thrust button. I prefer the plate, as the button often dictates what timing cover you use.
I strongly suggest pulling a valve cover and checking head castings. If they are the stock 89 TBI heads, they are the worst-flowing head chevy ever put on a production motor. Worse than 265 and 283 heads from the 50s. Quality power AND torque needs two very important things; head flow (both quality and quantity), and proper cam selection.
With heads, there are two things you're looking for: enough peak flow cfms to support the hp you want, and enough velocity to make good torque happen. You can have both, but it's not usually easy or cheap. Look at head port volume. Using random, round numbers, let's say you have two heads that flow the same 200 cfm. That flow suggests you can get X hp. One of the heads has 175cc ports, the other has 190cc ports. Every time, I would choose the 175cc ports. This means that the velocity of the intake charge is much higher which (along with other factors) means that low end torque will be helped. Airflow through an engine is partly about inertia and harmonics. A small, fast-moving column of air generates inertia, which means in a certain RPM range, the inertia will keep filling the cylinder even after the piston stops moving at BDC. The whole thing is a dance. You get the right volume of air moving at the right speed, then select a cam that closes the intake valve at the right time. Close the valve too early, (cam too small) and you miss out on that extra air. Close it too late (cam too big) and the air starts bouncing back out. (which, incidentally is why big cams have a lumpy idle). As you can imagine, this is why cam "size" reflects the RPM range. The physical properties of the moving air don't change, but as piston speeds increase, that intake valve closing point needs to happen later and later as RPMs rise. So a bigger cam matches the intake valve events to trap the most air during higher RPMs.
Big ports means slower air, which means you have to rev it higher to achieve that peak air-trapping. The holy grail is smaller ports that flow a lot of air so you can have the best of both worlds. Adequate velocity during low RPM, and adequate mass flow at higher RPMs.
The TBI heads (if that's what's on there) have small ports with a big swirl vane cast into them like a bent shark fin. It's designed as an MPG/emissions thing to keep the air and fuel mixed well. They are an example of great velocity, but terrible flow. They make pretty good torque in the low RPMs, but they are running out of breath by 4000 rpms.
For a street/truck/light towing vehicle, I can't imagine a better head than stock Vortecs. Aftermarket castings are cheap and less crack-prone. This assumes you have flat-top pistons. If you have dished pistons you'll get about 8.5:1 compression. Flat tops will give you 9.5:1 or so and a great platform. Pair that with something like a Melling 22135 cam (206/213 duration) and you have a recipe for around 300 hp with a torque peak at around 2600 rpms.
The Vortec heads have a specific intake bolt pattern and slightly higher ports, so you need a Vortec intake. You'll find that vortec carburetor intakes tend to be expensive because they're a "specialty performance" item. Easy solution: Find a marine junkyard. Marine engines used carburetors on Vortec engines for many years, so dead boats have lots of them. You can usually get them for $50 plus shipping instead of $300 from Edelbrock. Many of them on Volvo Penta and Mercruiser engines were actually the ZZ4 intake which is a great piece.
If, on the other hand, you pull the heads and notice dished pistons, we'll need to have a whole different conversation.
