It sounds like you're setting yourself up for a world of heartache friend. If you look at trucks that have 3" drop coils the spindle end of the lower arms are already way higher than the center of the crossmember. Not to mention you will have to be careful whenever you jack up the truck to make sure the front coil doesn't fall over (I know everyone doesn't have that problem but a lot of them do). Your balljoints are going to be in less than perfect geometry as well. If you want 6.5" of drop in the front and expect to have any reliability you are probably going to have to step up to a fatman or porterbilt rack & pinion setup. Or you can get out your favorite cutting tool, straight edge and welder and Z the front half of your truck. I'm not saying what you are suggesting wont work but do your research before you shell out the $ for your plans. As far as combining a 6" spring with blocks out back goes, be prepared for some more cutting. I'm running a 6" drop in the back and I feel I could benefit from a notch. The problem is that even with a notch you are still going to create other areas of interference. The bed floor is going to become an obstacle as well as I think at least one crossmember. Again I'm not saying that you can't go this route but form a good plan and decide what your level of committment is. I personally wanted my truck to be semi level and the rear to be as low as I could get it without having to use a notch. Anywho I'm off my little soapbox now!
Take your time and good luck!