Check your manual for output specs on your hydraulic system. You may find it is not 32 gpm. With hydraulics that's not a show stopper because lower flow can still do the job. You should verify the hydraulic output of the SEE/419 and match the motor to that output. You probably won't get 43 HP out of it. The 3000 psi is the max for the motor, and there again, the 419 may not have such a high rating.
In case that does not add up, consider that the PTO motor is expected to turn at 540 rpm. A larger displacement motor will require more volume of juice to accomplish that speed. A smaller displacement motor can accomplish the same output speed of 540 but will require less volume (this volume should match the 419 pump output) but provides less horsepower.
BTW, my experience is not with a 419 but with a 406, somewhat different animals. I would hate to confuse the issue but think most of the functionality of the 406's is similar to the 419, with the 419 being the more robust of the two!
Here's a possible idea for a three point hitch. On the German agricultural Unimogs, the two heavy/lower arms of the 3 point hitch come off the rear axle, not off the frame of the Unimog. The SEE might still have the bosses on the axle to mount the 3 point arms (legacy from original use of the axles). 3-point stuff is commonly available in Europe and several US importers can get it for you.
If not, there are tow bars which I have seen here on SS that use chain clamps to attach to the axle tubes. A pair of those axle clamps might be adaptable to 3-point arm mount brackets (with a little SS engineering). Then you would have to mount a lift cylinder off the back of the 419 frame, and that seems straightforward. Do some searching on Unimog 3 point and you'll find lots of ideas.
This will get you started:
http://www.benzworld.org/forums/unimog/2487873-unimog-3-point-hitch.html
Benzworld/Unimog is a wonderful site for Unimog enthusiasts. Once on the forum, use the 'forum search' feature and "3-point", or other terms. That'll keep you busy for a week.
Bob