engine swap

we have a 92 gmc sierra short box, reg. cab..it has the 4.3L v6, 5 spd tranny....my question is how hard and what would i have to do to swap in a 350?

Don't know about your state but in NC it won't pass emissions test if you swap at least that's what I was told by my mechanic who is also a NC inspection station.

This swap is not that bad and done quite often.
The 4.3 is a 350 minus 2 cylinders, though the only swaps I have dealt with personaly were auto trans, but those were a perfect fit so I would imagin your manual would work just as well.
The fitment of the engine itself only required the change of the mounts to the oem small block units.
As for the electrical, it's all there and the same, computers are the same but the computer chips are not, you will need to replace the chip with one out of a truck equiped like yours will be, "350 manual".
Of course the exhaust will have to be worked on but that's about it.
Your stock springs should have no problem with the extra weight of the 350.
Your original accessories should be a direct fit as well.