OK....I have made another discovery.
On the 1978 CB750 PD carbs with accelerator pump the floats are rectangular plastic.
The Clymer's manual does NOT show this style at all in chapter 3 or in chapter 6.
The measurement is 14.5mm above the carb body to the top of the float when the carb is upside down. OR .570 thousandths of an inch.
But you do not even need to measure. Just place a straight edge over the top of the idle jet (push in style) and you will see that when the float is .570 above the carb body surface that the top of the float and slow jet are the same height,when the carb is upside down. Do not push down on the floats to make this happen.
You do not have to worry about the float pressing on the float spring. The spring is so stiff that you would have to push it down with your finger to make a difference.
Check to see that the float bowl drains on the inside carb and the outside carb on each side of the bike point outwards.
I have seen several bikes now where the #1 and #4 float bowls are mixed up and point the wrong direction on the outside carb.
The float bowls on those two carbs will interchange.