Yes, you'll be fine. I'd recommend trying out walking with full rucksacks first to get used to them.

Also, if you're buying new rucksacks, make sure that you get someone in the shop to adjust them so they fit you comfortably. If that's not possible, as a rule of thumb, if you're carrying heavy packs, you want as much weight as possible on your hips and as little on your shoulders as possible. Use the chest straps to try to spread the weight around a bit more.

Also, carry plenty of Compeed 'second skin' hydrocolluloid plasters in case of blisters - they are expensive but absolutely brilliant - you can walk on a blister if you have one on. The important thing with blisters, though, is to catch them early - stop and put a plaster on if it starts to rub before it gets worse!

Hope that helps.