A friend of mine has a new set-up for a 65 Chevelle with 2" dropped spindles and single piston calipers with backing plates and hoses.
I have a drum brake set-up. Besides adding a booster, correct master cylinder, and proportioning valve and maybe the frame hose brackets, is there anything else that I would have to change?

In other words will a 65 work on a 68?

The dropped spindles are not year specific I'd think. The whole enchilada should just swap over to your '68 no prob. I'd put in new ball joints while you have it apart. Most of the brake system swaps out there will work on '64 thru '72. :D