Look at MackPack
I just installed a mackpack (www.macksails.com) on my 37c. I looked at the StackPack, but I was told my main needed to modified to put in the lazyjacks (they are integral). While this would provide finer control when dropping, it also increased the cost substantially. I spent $540 for the mackpack, and it took me only 2 hours (with one other person) to install. My father -in-law has one on his Hardin 45, and it works great, so I gave it a shot and I love it, and now I don't know what I would do without one (BTW, I don't work for Mack).