Thats a good question Jim. I know I told you that when I first did it I didn't really like the way it felt, but after I worked out a few things (new booster hose and a complete bleeding;I had one bleeder screw that wasn't working,etc). Then everything was awesome. I've got a set of new pads and new rotors which I'll probably install over break. I can't wait to find out what that will feel like!! The rotors and pads that came on the car are really shot so I know that with new ones it will stop on a dime. Basically I love the fronts only boost set-up it just needs a little tinkering to get it where it works good. Even if I had a working booster for the rear I probably wouldn't use it. I think you're doing the right thing with yours front boost only is the way to go!! Theres a guy in the St.louis club with a beautiful 69gtv thats been $$$restored he totally bypassed his boosters because he says you get a better pedal feel. IMHO having only the fronts boosted feels like its made to be that way.
I can't wait until your car is finished that 68 is one rare and good-looking machine!!