35a on a 750w Bafang G060 (fat) motor, with a 52v battery, is going to work great. Its a very commonly-used combination. I have done it with a twin-hub awd bike, so that means two 35a controllers and two motors. Acceleration is so fast you need to take those KT controllers and set them to full amp output with slow-start. And acceleration is still fast enough to make you smile.
The difference between the 3-pin and 9-pin controllers on Bafang motors is not cheapness of the 9-pin. The 3-pin is for the 48v hi-power 750w motor that can be taking in a lot of power, while the 9-pin is for the 250, 350 and 500w motors that can be using the lesser 36v or 48v, and lesser controller amps like 17-25. Both are just as water-resistant.
Swapping controllers like this is likely to involve a lot of chasing of one's tail as the real issue is matching the plugs for each item. Matching the motor plug, if anything, is the easy part. You want HIGO/Julet plugs to match one for one, or if you are unlucky you'll need to match up JST plugs.
@TrimmCreateBuilder mentioned he had a C961 display and thats not going to work with a KT controller. KT controllers need a KT display because the controller's settings interface is set by the display. And if its not a KT, it won't have the settings interface. A C961 is a Bafang display with a Bafang controller settings interface.
The controller pictured in Post 1 is a Lishui. Maybe google "LD Controller" and you can get pretty close to your original out of the gate so you don't have to buy all new other stuff to go with it. This one looks similar and there is a controller-only purchase option.
This is the controller set for EUNORAU 48V1000W hub motor kits, it is only working with 1000W gearless motor kit , so please check carefully before you buy. Electric bicycle conversion kits 48V 1000W brushless non-gear hub motor kits system Packing list: 1. 48V28A sin-wave controller for...
eunorau-ebike.com
(but a KT controller is going to be a far better product and you might be better off pulling everything out and replacing so you can get one of them to power your motor).