i myself would keep the stock engine at the least. once you get one running well, they will purr like kittens (which i am yet to hear a kitten purr, but you get the point) i myself think that the newer chassis ruins the personality of the truck, but if you are using it for highway or something of that sort i can see it. the stock setup is a little of a handful, but even just that 100 HP is still more fun than most v-8's in modern cars. it's just my 2 cents worth.
FYI: there are ways to make the old powertrain more road friendly, such as rear end & trans swaps. if you want to learn anything on the rear end swap, send me something! i did it to my truck, and wouldn't turn back! has stock 218 with 3 on the tree.