I am not sure what the latest changes are for the ZL-20, but will tell you what I did for an earlier version.
Rear Mount:
Check to see if you received longer bolts for the side mount. If not, remove one from the side covers, and get eight bolts that are same thread but about 3/8" longer (thickness of new mount). I mounted each part (3 piece) loosely until I had all bolts started. The under piece has to get around the hyd lines. Don't forget the bolts underneigth that go into bell housing. Once you have them all started, begin tightening them all down. I would tighten each side, then the ones under the tractor, thaen repeat until all were tight.
Front Mounts:
Probably different than mine. They would have changed for the wider recessed battery frame. There should be an angle to them. They mount such that the angle would meet out in front of the tractor. ie mounts are not the same or swapable. Probably just four bolts on each mount to frame.
Frame:
Check all grease fittings, sometimes they didn't drill the holes all the way through. If you see any bad welds, easier to fix before you mount it. Mount the bucket with the four large bolts/nuts.
Placing Frame on tractor:
Need two people for this. And you should be on flat level ground. Many have used a chain hoist, and it is probably easier than the method I used.
I filled the bucket with cinder blocks, and strapped it in so it couldn't slide out. The newer ZL20's have two posts to hold the frame up, mine had one, which was a balancing act. The posts need to be in place, and I might have done that before adding the weight to the bucket (memory bad?).
I then parked along the side of the fel, shut off tractor and hooked up hyd lines. Restarted tractor, and here is where you need the second pair of hands. You need to feather the hyd controls to get the fel into position, such that you can drive under it. Jerky motion will get the fel moving too quick and possibly out of control. The second person is holding onto the frame and keeping it from tipping. Once you have it up to height, put some 2x4s under it, shut off engine, and disconnect fel hyd hose, and connect for just tractor. Use your creeper gear to postion tractor under fel. It will be a tight fit on the muffler/fel control side. Once I was close enough, I shutdown engine and reconnect fel hyd and restarted. You will probably have to make small changes in heght to get into the rear saddles. Watch to make sure the front part of the frame is on the correct side of the front mounts. When positioned correctly, pin the sadle mounts. There are large nuts that when you tighten them down, pulls the fel all the way into the saddle. Align the front frame to the front mounts such that you can get all four bolts per side.
Its a pain, but take your time and make sure you have the second safety person. A chain hoist is probably the better way to go and safer, if you have that option. I didn't and this is the method I came up with.
