Definitely a BT. The carb base has been worked perhaps on a flow bench.
If you go for a 750, you will need something more then a stock CJ camshaft otherwise you are wasting your time with it.
I find that a 4779 750cfm double pumper (with mechanical secondaries) works better then the generic 3310 with vacuum secondaries.
Both will give you the same top end power but the DP will give you better throttle response.
Actually I personally found the Edelbrock Torker more responsive then the BT. I felt that the BT was better for an automatic transmissioned car and the Torker better for a manual.
I'm not talking about ultimate horsepower, just throttle response.
The BT has 4 good flow ports and 4 that need flowbench work. Look inside that manifold at the runners. Do you see grinding marks? It looks like it has had work done to it.