340 carb size

The 750 will be big on the primary side. The 68-70 340 had a small square bore carburetor. The 71 and up had the 850 TQ and they worked WELL. Making that comparison, the squareness of the 750s venturis will make for some tuning on e stock bore and stroke 340. I would start with 2 steps leaner on the primary jets. You may be able to step up the secondaries, but I would concentrate on the primary side first.