273 swap to 318/ build, cost, potential, daily driver

I say this with all the fellow car guy love I know how so don't take it personally. It sounds like you want someone to lead you by the hand through this. That ain't gonna happen. You are going to have to make up your own mind what you want and how to go about it. We're here to help with things if you get hung up on something, but we can't make your mind up for you. I know what I would do, but whether that meets your wants or needs is anybody's guess.