I've heard of the sway bar problem before. But I did install hooker headers quite a while ago without having the swaybar issue. Those headers had the wrong flange port position for my 390. The emmission era heads changed exhaust port position and headers made for older FE's will leak...I found this out the hard way. Had to go back to the Ford stock manifold.
I'm trying to figure out what the problem is with the swaybar....mine is positioned a little lowerer than the cross member. And the exhaust pipes exited the header above the cross member. I did have headers installed and the swaybar wasn't an issue...am I missing something here? The only problem with those headers were the wrong flange for my later emissions head.
I read your post about Headman headers. Were they installed on FE 390? Do you remenber the part number? I'd like to go with 3/8" flange this time. Flat fit without the "raised weld" around the port type. Are your Headmans like this?