I know you die hards say that ya gotta have bushings, but I have done this in many cars in my career with success. There should not be much flex or hop in the mustache bar - right? There is usually enough rubber (hopefully not dry rotted) to provide a decent cushion against the rear frame of the car. I went to the local hardware store and got 8 large washers and pulled the mustache bar. I put 2 washers between the frame and the mustache bar and put the bar up, then put 2 more washers between the bar and the keeper (also has rubber bushing) and then bolted it all together tight. The rubber squeezes up against the washers and provides a certain degree of cushion against the frame.
Call me crazy - call me cheap, but for $1.94 at Ace Hardware, it works just fine for me!
I know it seems like alot to pay for some rubber, but come on, if you replace them now they may have to be replaced when your grandson takes the car autocrossing. I replaced mine and they do make a difference.
Talk about cheap, back in my younger/poorer days, I cut two pieces of rubber out of an old tire sidewall, put holes in them and used them to shim up the bushings. It sounds crazy (and stupid) today, but it was free and really helped alot back then.