I have a TR250 engine in a '73. I had to use the older style manifold with the ERG valve. Given my 73 is exempt from California SMOG inspections, I simply blocked off the ERG valve and using the carbs from the 73, set up the emission control system as if it were a '73.
If the 72 engine has the later style head, you are in business.
But if the engine you are getting has the older style head, you will be using the older style manifold, and the car may not pass the visual part of the SMOG inspection in Calif. However, you can refurbish the 74 head, install it on the 72 block and use the 74 manifolds. In no time you will be back on the road and the car will pass the emissions test in CA.