This is the Curtis plow mount on my 04 900. The tongue on the plow goes into sloped area and catches on the horizontal plate. The two levers with the ball ends go into slots and hold in the circular area on the ends of the slots.
A couple of pins hold the ball mount levers from moving. Let me know if you need some more shots. Also, spray the mounting hardware on the machine with fluid film, it helps the install and reduces rusting.
This all it takes to mount the plow to the machine. It looks like you scored the hydraulics too. I now wish mine had them also.
Here it is mounted.
BTW, it looks like your mount is a scoche bent, I'd try to get it straight before I'd install it. The plow fits relatively tight to that lip. Just try it before you bolt it to the machine to be sure you can draw the plow tight to the hitch with the lever arms.
I may have gotten a little wordy but to answer your question about the mount surface on the machine, I'd BFH the area back to even and weld it up after pulling the plastic guard. My guess is it's fairly unusual as most of the force from the plow is straight back.
P.S. I do have an owner manual but it lacks the hydraulic connection data. I could email if necessary
Bob