The 7 backhoe is a bit different than the 448 in attachment. There should be a sticker on the hoe that outlines the procedure. If you don't have that, I'll try to describe here. If that fails, I can post some pics, scan some instructions or whatever you want. I have a 7 on my 790 which is the same tractor as a 770.
All of this assumes your tractor has the Power Beyond and tractor-side mounting brackets. If not, it will never mount.
First, remove the three point lower arms, lift links and top link. There is a locking bar that will keep your rockshaft arms in the up position but I'm sure you can live without it.
Back the tractor up over the hoe until you can hook up the hydraulics. Once hooked up, raise the hoe using combinations of stabilizers and boom so the lower mount is even with the tractor bracket (height) and the front of the subframe is tipped down somewhat. Back up to engage the rear lower mount in it's slots on the tractor.
Again using a combination of stabilizers and boom, lower the rear of the hoe. It will pivot in the rear mount causing the front to raise and engage the forward subframe mounts. They should self-latch (make sure they are unlatched beforehand). Once latched, raise the rear again and hook up the upper mount to the top link hole on the tractor.
That's it. On a good day I can do all of the above in under five minutes! Raise everything up and you're off to the races!
Let me know if you need anything more. I have manuals and such at home /forums/images/graemlins/smile.gif