Customcab: If it's stored inside, the red oxide primer will hold up. But if you want to seal it use an Epoxy primer.
I always like these old trucks, I think the styling is better than some of the current models. I would love to be able to stretch the cab about 6"-8" to give more leg room and storage. Then stretch the frame the same about so every things matches up and you still have the full size bed. It will also turns some heads, particular the old timers that know that's not factory.
Paint gives a truck character, make it unique as you like.
So there is no bad paint job unless your making a show truck. $20,000 paint jobs are not daily drivers and are only good to look at. I rather drive mine. Just take your time, you will come up with a idea that suits you and yours wants/needs. Don't ever cut your self short, you will be surprised at one can due if the need presents it self.