You can search around for reman valve bodies, but I prefer to have the valve body from the car reworked rather than installing something that my be tuned slightly differently than what is in your car.
I used Pacific Coast Transmission
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for my 6 speed rework. Johnny was a really good guy to work with, they usually turn the valve body around the same day or the next day. Nice packaging on the return, they warranty their work for 2 years and they use an engraver to label all the solenoids and parts they rework so they know "they" have been in the valve body.
This was one of the few places I contacted that offered an exchange valve body, but agreed if I would have the down time on the car, that reworking my current valve body was a better option. So this is another reason I went with Pacific Coast over a swap house.
Search around and ask any of the shops you contact about the transmission wiring harness for the 4 speed. Many suggest replacing the wiring harness in the transmission, not sure if this is due to connector problems or what the issue is. I did not change the harness in my 6 speed. I know the solenoid connectors are a bit small and tricky to remove. I also tightened up temp sensor connector and another detent connector a they seemed a bit loose.
Also take pictures of the wiring to the solenoids and mark them as needed. Although you only have a 4 speed, still a lot of wires and wire supports and they need to all go in the correct location. It will save you A LOT of time when you go to reassemble.
A BIG suggestion if you do the job yourself and have a scan tool, before you put the pan on, turn the ignition on and run the trans though all the gears without the engine running to make sure you do no get a CEL or have the trans shift indicator on the cluster show it in limp mode or a fault condition. It is easy to miss a connector or not fully plug a connection in on the valve body. If you have a connection issue, you will get an immediate CEL and likely have the cluster show the trans in limp mode. If you do this before you install the pan and fill with fluid, it will save you a lot of time!!!
Ask me how I know!!! The 2nd drain and refill goes MUCH quicker. Just a word to the wise.