Classic/Antique Car Repair: Tranny bouncing???, pop pop pop, loose bolts

Question
I have a 69 gto and recently when I hit the brakes, there's a pop pop pop sound coming from the center of the front floor pan. Checked the tranny mount, and was decayed, so I replaced it, but its still doing it, just not as bad. Checked the exhaust, its not hitting, made sure the transmission crossmember was tight. Thought about the e brake cables but they wouldn't be hitting that loud. Do you think this could be weak motor mounts or loose bolts on the tranny/engine allowing one or both to shift when braking? Body bushing problem? I know she needs new body bushings, one has tilted and 1/2 through the top rail of frame. I'm stumped and ready to use it as a extremely nice parts car for my other 69 and 68.
Thanks in advance for any help you may be able to give, I appriciate it,
Sean

Answer
You could try replacing the front motor mounts, but my guess is that the body has settled down too low, and is going to hit the back end of the engine/transmission assembly during braking, because that is when the engine pitches forward a bit and allows the transmission to lift up off it's rear mounts.  If you have rust problems causing the body mounts to sag through the metal, I think it's time to do a complete restoration, or else, as you say, use it for a parts car -  sorry I can't come up with a brilliant suggestion.

I guess you could try just putting a thick piece of rubber, like an old tire tread between the top of the transmission and the floor pan, but I think your car has reached the point where it probably isn't really safe to drive anymore.

Dick