I am a great believer in going with what works for you.
I do a lot of walking and in my experience, when you are having a play with what you carry, the best thing to do is to strap your pack on your back, pop out for a wander and see how you go. If it works, stick with it and tweak if and when further inspiration hits. If it doesn't, try something else.
I'm a shortie shoulder hauler and the hip/shoulder weight distribution designed into bigger packs, just does not work for me. I am most comfortable carrying the bulk of my pack weight on my shoulders and upper back, as is the case with an ALICE style bag, with sleep gear attached underneath level with my hips. Lots of people have told me that, this mode of carry is wrong, but it works for me and I am not troubled with back problems, so I'm sticking with it (indeed I'm just starting a pack mod, that will tailor my pack more to my preferred mode of carry).
I did a 30 mile (ish) circuit around my little corner of Cornwall on Tuesday. I wasn't carrying anywhere near the weight you are intending to haul (I had no more on me than 10 pounds tops) and only had a 25L day sack strapped (high) on my back. I was only intending to do a 16 - 18 miler, but I got my walking head on and instead of just hiking There, I decided to hike Back Again too. It was a bit beyond where I thought I was at, in terms of endurance, but apart from a little stiffness yesterday, I've no aches or blisters and I'm gagging to get out do a 20 - 30 hike again. And, it was good practice for a couple of hiking adventures I hope to enjoy later in the year.
What I do when prepping for an adventure, and this might work for, might not, is forget about the weight in the first instance and focus on the distance walked. Then when I'm happy I'm covering the desired distance at a fair clip, I up the weight, gradually (once tried going straight from training with a daysack, to training with a fully laden rucksack and it was not a happy experience) until I get to the point where I am walking the distances I hope to cover each day, hauling the weight I intend to carry. It works for me.
But it sound like you have your training pretty sorted, so I hope you can endure your practice sessions and enjoy your adventure.
I hope you have a grand time.
Good Luck,
Colin