Squarebodies are not investments brah. Sorry to be the bearer of bad news but it's true. If you want out of it, as said above, just tweek tune it a bit so it runs good and sell as is. Putting $1000 in parts to do updates, might net you an additional $300-$500 for the truck, so your out $500-$700 in cash not to mention your labor. It's certainly a good project truck, but you'd only restore it for your own self satisfaction and nothing else, but not an investment that will have a return, because it will be a big loss and disappointment, not a return at all.
Usually when we talk about, "Flip this Truck", it's cuz we rolled it and it then goes to the junkyard.
