It also depends on what you want to do with the truck. Like it or not, some mods HAVE to be done just so the truck can stay up with today's traffic. With the inline six, in stock form at least, they are extremely slow. To build one up to outperform or at least perform as well as a V8, you're going to spend a lot of money, probably more than it would cost to drop in a V8.
I do agree that a hopped up stovebolt engine is a lot cooler than a V8. So if you want the cool points, you can't beat a beautiful inline 6. Especially if it performs halfway decent. I'd say if you're cruising it or showing it, you might want the straight six.
If you want practicality or actually plan on using your truck for work or towing, then you should consider the V8. I don't think gas mileage is an issue, they both get pretty bad gas mileage compared to each other. In this case, the superior torque and higher redline of a V8 would be preferable. And you can make a V8 just as beautiful in an old truck as you can a stovebolt.
I'm surprised more people don't look to power-adders such as turbochargers or centrifugal superchargers to improve the power of an I-6. You would EASILY be able to outpower a normal V8 with a blown I-6. I'd like to experiment with that myself, but I need warmer weather to do it.
