Welcome Curtis. I sure don't have a problem with you pulling out the original engine and putting in something more modern. I have two '58s, a Chevy and a GMC. The Chevy is bone stock and the GMC I'm building into a little hot rod. Just make sure you don't scrap the original engine and trans. Somebody will need that stuff. It's getting harder to find and we have to save some for the next generation.
BTW, Nice truck! Keep us posted.