Putting a 350 in one of those trucks is not a "drop in" kind of deal, and i've not heard of a "package" or "kit" for that purpose.
Most folks who've done that conversion mention having to move the steering box, and having to do some chopping under the hood to get a bigger radiator to fit further forward.
Here's a link in the Tech Tips section to an article where a fellow swapped his stock 216 with a GMC 302.. not exactly swapping a 216 with a 350, but I would guess the same issues need to be addressed in the swap (perhaps just not with the same solutions)
TechTips Article on 216 to GMC302 swap
