You can use the stock radiator if you use the 273 water pump and timing cover. If you use a 360 pump (recommended) you will need the 360 timing cover and a radiator for a 1970 or later A body. That's in addition to the torque converter and mount issues already mentioned.
273 timing cover has the bolt on tab for the timing marks & it positions it on the other side. He will need to use the 360 balancer so the marks won't work. Gonna have to use the 360 timing cover too.
