no, the 4.3 will drop right in after you swap motor mounts.... GM made everything you need to do this, hence the 4.3 motor in the s10s.........just find a donor and take all you need
youll need a 4.3 tranny which you know if you already know that the 2.8 isn't the same bell housing as the sbc
if your using a 700r4 the tranny cross member will be in the right place and every thing should bolt up no prob.
i put a 4.3 in my and made if TBI, was an 84.... it took me two days working completly by myself to pull and swap the new motor in, including the wiring...wasn't bad at all..
the motor mounts are the worst, you have to drop the lower control arms to get to the nuts....you dont need to remove the springs or anything just the lower control arm pivot bolts and reach up in.... no fun by yourself.
i had to swap out the condensor, evaporator, rad, rad overflow tank, motor mounts, and the y pipe........ from 2.8 to 4.3....... they were all different
finding a donor truck is the way to go