Saw your message in the other section - which 3000 was it on, 3 or 4 cyl?
I hear the biggest worry is the upper link bracket on a tractor - they break off.
Do you have a loader on your 800? Is it a pto pump with the backhoe, or run off the tractor?
I don't believe a 3000 is any stronger than an 800 on hp, but the engine isn't the important part. You need to compare bracket & tractor frame strenghth, hyd flow, and front ballasting.
What model of backhoe, that would probably get you the quickest answer?