welcome! If your 273 is original, the water pump will be cast and exit on the opposite side as a '70 and up 318. Also, the timing marks will be on the opposite side. A few ways around it, one being a different radiator.
yup, or you can swap over your old or same style water pump / timing cover. that way all the brackets you have will fit. if you change to a 70' later WP, getting the matching timing cover and accessory brackets will be a big help
