Carb plenum, inlet .dia CFM calculation?

well measure the diameter os each barrell, will be something like 1 3/4 inches.
1.75 inch has an area of 2.4 sq inch. you have 4 of these. so you need a total of 9.6 sq inch minimun.
a 3 inch pipe has 7.06 sq inch, so 2 of them will have over 14 sq inch, basically 50% bigger, less bends and so on, tells you it will be fine.
Also i think your throttle bores will be LESS than 1.75 inch each.
hope that helps
Paul