i'll cover some of what has already been said & then add to it, for me its the easiest way. so this will be a little long, sorry.
carburetors and TBI each have their own advantages.
with a carb there are few wires to mess with & most people feel they are easier to repair when there is a problem.
with TBI, you have more wiring, some sensors & the ECM to contend with.
but with TBI working right, most people get better fuel mileage & overall better driveability.
to go back with a carburetor on the TBI motor would be easy. you would just need to get an intake to fit the heads or modify your old intake.
like has been said, to put TBI on your 84 you need the TBI unit, distributor, ECM, harness, knock module, & all the sensors.
you'll need a vehicle speed sensor (VSS) of some kind, but thats not too bad of a problem.
you'll need the fuel pump, i believe the sending unit from the 87 suburban will fit right into your current tank, but i could be wrong.
you'll need to run at least 1 extra fuel line for the fuel return.
if you don't run a new metal line for the pressure side, you will also need to change all the rubber hose on your factory supply line to rubber hose rated to handle higher
pressures and make sure you use good screw type hose clamps. some stock TBI fuel pumps can produce up around 25 PSI dead head. TBI needs around 13 PSI to run right.
if your good with wiring, it shouldn't be too much of a problem to get it wired up, just time consuming.
you will need a good book that covers the system you have.
for the check engine light, you can add a light or you can use one of the used lights in your instrument cluster.
you'll need to learn how to trouble shoot & repair it when you have a problem.
GM used the 700R4 till around 91 or so, & then it was called the 4L60.
both only have the torque converter clutch or TCC controlled by the ECM.
you can still use the 700R4 or the 4L60 without a computer, you can get a kit to control the TCC.
i believe it was 93 when GM started using the 4L60E, which must have a computer to control it.
it depends on which 350 transmission you have if you'll need to cut the drive shaft or not.
you may also need to make some minor mods to the trans cross member.
the 87 motor you have was called a Vortec, but don't confuse it with the later model 96~02 5.7 Vortecs.
in 87 on the TBI motors GM used swirl port heads. they aren't the best for all out performance, but they do help out with torque. with the right cam those heads work really well in a pickup.