This is my 13th season of using double blades, so I guess I would qualify to answer this one. Yes, you have plenty of power to run double blades. I've run them on 60" DC's with only 20 HP Magnum engines and they handled the double blades just fine. I run a high lift blade and a Gator blade, both for 60" Choppers. You can use 2 sets of regular lift blades, a high lift and a regular, which ever you have laying around. The top blade doesn't even need to be a new blade, a worn out one will do just fine, because all it does is chop up grass clippings more. The bottom blade does all the cutting. You can get brackets, but you don't need them. I have a set of brackets now, but went for 12 full seasons and part of the 13th without. The only time they will move is if you hit something solid and if you do, just loosen up the bolt and adjust them in the + possition again and away you go. If you use a gator as a second blade, it only slows down the rpm's about 50 rpms, so it's not a big deal and the cut is worth it. They also are great for mulching leaves. I have an article on my website about double blades if your interested. Just make sure the bolt has at least 1" or more of threads to screw in the spindle and if you ever shut off the blades to scrape a deck, make sure the blades have come to a stop before putting your hands underneath. The blades will take a longer time to stop with double blades on.
I put on a set of mulching chains on my diesel Chopper today for the first time which are supposed to help with leaves and clippings. It is a bracket that has 2 short chains on each spindle and are 3" above the bottom of the spindle. I also have the double blades on so I am going to chop the leaves up big time this year. With this set up I'm not using the brackets to hold the blades in a + possition. The leaves haven't gotten very thick yet, so I'll report in on how this works later on when they start dropping more. Good luck and if you have any more questions, I'll do what I can to answer them. If anyone has an interest in this setup, I'll post a picture of this combination so you can see it. I've taken the picture, I just don't have it uploaded yet.