If it still has the TBI distributor ( remote coil, no vacume advance) in it it will run like crap. It needs a older model HEI (coil in cap) Dist to work right.
Also the TBI fuel pump(If still so equipped) delivers too much pressure for a carb. It should have a regulator that will allow no more than 6 psi max. Also I think the pump will eventually go bad unless it has a return line plumbed back to the tank.The pump is cooled by the fuel flow.
As for putting the fuel injection back on. You need to make sure that all the connectors/Fuel lines(supply and return) for the Throttle body and various sensors and controlls (there are quite a few) are still on the engine. Or come with the new manifold/TBI You will have to get a stock or after market TBI manifiod. Everything and all sensors must be hooked up properly or it wont run right.
Yur probabally better off trying to make the carb set up run right than converting it back unless you really know what you are doing with FI.