I have allways used SU Carbs on them old Knuckles and Pans.
The problem with the Bendix is the accelerator Pump and it`s related parts.
It is leaking Gas sooner or later and the pump is not adjustable. With the SU you may have to kick it once more but it runs smooth as silk. But you have to adjust it right.
If you consider the SU let me know and I´ll help with adjustment Instructions