Soz, can't help with Al. shock towers.
Aluminum big bores are not any better on the leakage from most reports than the standard big bores. They also have a further disadvantage in that the o rings are in a cartridge and can't be cleaned properly without breaking the cartridge open if I remember correctly.
I've found stock plastic big bores do leak a little but i get away with 6 months or so of bashing before i need to top them up. Have been thinking of tracking down some alternate o rings as I think they are the prob, the design is ok.
Haven't read much about experiences with the new Innovative shocks. I do know they are very heavy(~100gm per shock over stock big bore) which is worth considering. They also require the Innovative shock tower mounts. I've used these and they tend to destroy your body where it hits them.
As for diffs, try some Vorza diffs. These have the slightly larger hot bodies internal gears and a cup that allows for a 8x16 bearing instead of 10x16. Just fit Flux out drives and bevel gear.
http://www.rc-monster.com/forum/showthread.php?t=29113