Arc Navomatic components

[YankeeClipper]

Are the servos used with a 400 the same as those for a 400A or 400B? The later control units come up often on ebay, and I see there are still a few repair facilities out there that will refresh them. So I'm wondering if it would be feasible and practical for me to upgrade from my 400 to the A or b. I'm not sure but I think I would also need to upgrade the computer or amplifier, but would there be anything else I would need to consider?