M didn't have two 12.7mm guns?
No, it did not.
M and T was basically the same airframe, cockpit moved 400mm aft. M had however more fuel, 650 litres vs. 440 litres, like Yak-9D.
AH Yak-9T (20mm) has less weight to compensate the difference, though.
They have got it right, as usual.