second across-the-line starter

Hello group, long time reader first time writer.


Situation:
- Two 600VAC motors (yes, Canada) 200Hp, each driving common shaft.

Starter #1
- size 5 isolation contactor, soft start, size five ss bypass contactor
- each starter is a cubic, self enclosed, top-fed / bottom-load siemens contactor

Starter #2
- size five contactor
- this starter is more bulky, vertical lift, top-fed / top-load, three separate contact housings, furnas contactor

Typical startup
- isolation contactor pulls in, softstart ramps, bypass contactor pulls in on SS up to voltage, delay, starter #2 pulls in

1. I do not understand why starter #2 is a different style. I am unable to obtain original manufacturing specs and I am searching for a reason why not to replace starter #2 contactor with same style as starter #1.

2. Necessity powers my questioning as my starter #2 coil hums louder than most humans and is on its last legs. Furnas has discontinued this coil.

Possible solutions:
a) replace 600v coil with 120v coil which we seem to have in abundance.
b) replace bulbous contactor with other style, standardize inventory.
c) run screaming into the night.

Why would the factory use two different styles of contactors? Should not what is good for starter #1 be good for starter #2?
There are a few more cases of this example at this facility but with size 6 contactors.

Thanks in advance for criticisms / comments

- Monte Stevens