Highest LIft cam with 68 340 with stock intake and carb

Assuming "no" meant it's still a 340. I wouldn't put a Victor on a 340 unless it was in a very light full race car. If you also have factory HP exhaust manifolds then you're leaving a bunch on the table and a Victor is the wrong add-on. Headers, an RPM, and a decent carb and you're there.