Jeremy, A friend here has a 4.2 in his '60 Chevy pickup and likes it so much he is thinking about putting on in his '55 Chevy two door. I saw one in a '29 Ford roadster at the recent Inliner Convention. Efi-diy has one in a '50 GMC pickup and is a source of oil pans, cams, dampeners, and knowledge on these engines.
On the other hand a 250 or 292 L6 would almost bolt into your truck, well as easily as a 350. I own 3 vehicles with 350s and one with a 305. On one when the 350 wears out I will replace it with a 250. Another is scheduled for a 292. When those are done another 350 rig will be sold and the 305 truck will go for scrap. You have to know and love these engines to make it worth while. If as you say it doesn't matter to you and you are not interested in learning why we feel as we do then the 350 route may be for you.
Do some reading here and elsewhere. Be honest with yourself about what you really want your truck to be. As an artist simply look at a well fitted inline as a kinetic sculpture that is far more unique with more mystique than the over used 350 cliche. It is, in part, not about being different as much as about not being the same. Beater
