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

Take the path of least resistance, as in affordability and ease of assembling and installing without having to buy specialty make it fit parts. Your goal should be to get it on the road asap without frustration of a long build. A car of that age is going to have other work going forward, body work and paint, interior repair, brakes, tires and so on. It never ends. You don’t want to start a project and end up not seeing light at the end of the tunnel.