Doug's Headers in 64-66 A-Body

I use the stock style mounts, not the Schumacher ones. I have heard of the problem you are having when installed with the Schumacher mounts. I have a turnbuckle tie down from the left side motor mount to block bolt to the cross member and have a bit of preload on it. This is important as you see it is tight when the engine is not running it gets worse when you get on it. I have a 1.14 torsion bar running through the tubes and it just barely touches on both sides. Getting the hex through tubes involves hitting the end of the bar with a dead blow, you probably wont get it through with out. I have run this set up for more than 20 years with no issues and have had them in and out many times. Try the stock mounts.