The 68-71 340's have 2.02 intakes, 72 & 73 have 1.88... The bigger valves don't lose any torque so it really doesn't matter.... All original 340's have open chamber heads....
68-71 are rated at 10.5 but measure out to a true 9.6ish...
72-73 are rated at 8.5 but really are less than 8...