As far as being able to operate one brand of plow with a different make pump, yes it can be done - I use a Monarch pump for my Western blade. Lift arm hooks up to the blade with a chain, power angle cylinders use standard hydraulic hose/fittings.
Attaching a different make pump to your headgear may require some fabricating however - without actually seeing how different the two pumps are I can't offer any more specific info.
Just wondering the reason for making the switch - I went to the Monarch because I like the under-hood installation.
I was curious about pump interchangeability for an emergency situation.
I am interested in your Monarch pump retrofit. Since you mounted it under hood, I'm guessing you have 3 hydraulic quick connects for each of the angling/lift cylinders? Have you been happy with its performance and reliability?
Good thinking on "being prepared" in case of a pump failure. Do you have one of each pump now? If so, perhaps one of them could be used as a bargaining chip towards a spare pump of the brand you wish to keep.
No complaints about the Monarch unit. Bought it used 2 seasons ago, just had the pump overhauled (output pressure was a little low due to wear) and reinstalled it a couple weeks ago.
I leave my lift cylinder on all the time, so no quick connector needed there. One for each angle cylinder, male end on one/female on the other so there's no way to mix 'em up. I also have those little rubber caps to keep debris out of the truck fittings when the plow is off.
I was wondering about interchangeability from an upgrade point of view, since the Western plow I have has the old cable operated pump. The plow is a modified hybrid, in that it has the newer uni-mount hardware. However, the uni-mount isn't that much of an advantage without a solenoid operated pump!