No, the fuel injection pump will not work with a carburetor. I highly recommend you stick with fuel injection, but that's just me!! Your 86 block will work in your 89. I believe the heads are the same also, but I think the cams are different! And since you will have everything out, why not do a valve job on your TBI heads and use those?!?!
If you are going back to a carb, you must drop the tank, replace your fuel pump with a tube, and install an external electric pump designed for carburetors. You can adapt your existing fuel pump wiring to run the new pump!!
Hope this helps