The difference between the D600 and the much newer D722 is a lot, going to an D1105 would be way too much HP for that little skid steer.
Now could it work, maybe, a lot of size and mounting variables between the two.
Also note that upping the HP can be detrimental to an old skid steer.
The drives and pump could easily be damaged.
Also you need to find a engine that was NOT used as a power plant or generator as they will be a set RPM and not easily changeable to a variable RPM engine.