the 73 had flat top carbs but a good intake manifould, marked 36 , so what you need is the Round top SUs carbs and linkage to the firewall .Thats the "best" set up . You will get alot of debate on this , but for my money this it! All will bolt up to the manifold that are four bolt carbs. that is. I really think that injection is by far the most power producing but the most trouble in these cars . If you want performance and easy to understand and work on go the SUs , no doubt. Another really good mod. is a electronic ignition from an 79 .Its a easy install just look at the search and enter ignition up grade .
good luck , Gary Portland Or.
I keep seeing postings that you need linkage back to the firewall when swapping SU carbs for flat tops. When I made my swap, all I had to do was bolt the SUs on and replace the linkage BETWEEN the carbs with the early SU linkage. Getting the bottem bolts off the old boat anchors is a real mechanics nightmare, but the ease of the SU boltup makes up for it. There are a lot of vacuum and water lines to plug if you dont use the early balance tube, however, the flat top balance tube works fine with the swap.