[1QuickS]

Regarding the 36mm chokes vs. 40mm bore diameter with throttle shaft blockage: brain fart. Air velocity increases as it is passing waist of venturi then slows as it expands into diameter of throttle bore. Then the velocity increases as it must pass the obstruction of the shaft. This is at WOT.

40mm throttle bores will provide great low speed throttle response in larger engines but cannot support venturis larger than 36mm.

Low speed throttle response is directly affected by airflow past the progression holes while the throttle valves are almost closed, this is referred to as the "Low speed circuit". For a given engine, smaller bores will have higher air flow velocities past the edge of the partially open throttle valves as compared to slower velocities of larger throttle bores. Higher air flow velocity generates lower air pressure which sucks fuel from the progression ports more effectively than lower air velocities of larger throttle bores.

Full radius horns can account for a few % extra air flow over the tulip horns of the Webers, something like 5%. What surprised me was the improvement in low velocity performance on my engine.

Tall air horns vs. short air horns in the triple Webers is only 6mm difference in height. I doubt any performance enhancement is detectable here. I think the tall horns were adopted when the tall auxiliary venturis were introduced to keep the tops of those below the top of the air horns. To gain significant advantage in height of air horns you would need inches of difference between tall & short horn height.

The newer style "hatchets" are actually from the IDTP Webers as used on the 1969 911T & 914/6. I know this since I recommended that Richard adopt them on his PMOs to help one of his customers overcome slow speed grasp. I also revised the progression pattern for his 40mm, 46mm & 50mm carbs. The IDTP "hatchets" have a steeper "ramp" than the standard "IDA" cam-levers but total lift is the same. So, total fuel squirt amount is equivalent in both types but the IDTP cam-levers deliver it quicker at a lower engine speed.

I thought we were discussing Webers. So now we are discussing PMOs? I think all PMO carbs use a 50mm top bore vs. 46mm for the Webers. The larger opening should provide a smoother inlet air flow than the Webers would. 46mm throttle bodies would probably be fine with 36mm chokes but you would not have the easiest path for good transition as with 40mm bores. If you have Webers already then you are ahead but they would probably need service. If they are 40mm bores and you wanted 46mm then they could be enlarged. If you do not have carbs then PMOs are the lowest cost path forward. I'd contact PMO for their recommendations on carb sizing for your project.