Towing on 26's is a bad idea, period. Your brakes are already stressed because of the added weight as well as your Transmission and rear diff. Now your adding more weight into the mix which is a recipe for disaster, especially on your transmission unless you're planning on rebuilding it often.
Also, depending on the weight of the boat, trailer, car, etc. The 26's aren't going to hold up to the heat and weight very well, especially if you hit a pot hole. I can almost guarantee a blow out/bent rim will occur which can lead to a harry situation quickly. I'm also pretty sure that you're not going to find a 26" tire that is a proper LT rated tire for the towing capabilities that you need. Most 26" are a passenger rated tire and are not meant to tow.
Unfortunately, like iambub stated, 26's, towing, comfort and practicality don't mix.
Don't mean to sound harsh, just looking out for you and your families safety. I pull a 19ft 1971 Hallett Jetboat which is by no means light and won't even think about going over a 22" rim as I know the brakes, trans and rear-end wont be happy as they occasionally don't like the 20's when climbing a steep grade. That's even with a rebuilt motor, Transmission and upgraded trans-cooler.
As for the drop kit, I'd go with DJM 2/3 drop kit with there stiffer rear springs that are tow friendly and helper bags. This is what I am going with on my Suburban and should serve you well with what you have in mind.
Just my .02, don't want to see you damage your truck or worse yet, crash.
