well your gonna have to do a good rebuild to get the 350 horse you want, that motor comes stock with around 290-300 horse, depending on the output, being a Z71, you might find it is a 300 horse engine, putting on a carb and getting rid of most of the NOX stuff you do not need won't get much more, and there not exactly good on gas, my friend has a '94 GMC Sierra GTw/ 350 3spd auto, and he gets between 12-14MPG, if the '92's trans is still available and is a 4L60E or a 700R4, you might want to consider trying to get that and the '92's driveshaft ( I think the chassies are the same, so the driveshaft would fit your '85 w/ the overdrive trans ).