Worth has nothing to do with this equation. The truck is only worth what someone is willing to pay at the time of sale. If the truck is running it will likely be worth more than if it is not. You will probably NOT recoup the cost of replacing an engine upon sale of the truck.
However, what you prefer does have bearing. I will be getting a mildly built 1960 pontiac 389 back from the machine shop in a couple of weeks. This engine is built for 400+ hp with a stroker crank. It will bolt in where the original gmc 336 was, and look almost identicle to the original gmc motor. This motor has cost around $4500 to build. My truck looks like it is worth less than $2000. This combination is worth more to me than others because I am the one who will be benefiting from the increased hp. The "ratty" looking rusty truck does not garner a whole lot of attention or interest from most sane folk. I am not sane!
