There are a several considerations with mounting a windlass. First, the windlass must allow for an adequate chain fall or the chain and rode will castle with the rode falling off the windlass.
To be effective the rode needs to wrap around the gypsy, typically about 180° around.
Next is the location of the motor. The gypsy that is seen above deck is only a small part of the windlass. There is a large motor beneath the deck.
There will be a lot of force exerted on the windlass. The supporting structures must be strong enough to handle the loads.
Finally, windlasses are designed to mounted on a flat horizontal surface. Some windlass have a vertically oriented gypsy, such as the Lewmar V700 other are horizontal. The rode on the V700 must wrap around the gypsy by about 180° before falling into the chain locker. It will be impossible to do this if the wlndlass is mounted on a vertical surface.