What modification must be done to the (67) clutch Z-bar in order to install some headers. I looked from underneath and it doesn't look like any headers could fit...the z bar and its return spring take up most of the room.
I have no issues running hooker comp long tubes and the z-bar, although I have a 65, I dont think there is too much difference between the 65/66 linkage to the 67/68
I've seen this on some cars, but not all cars. There might be a slot and a small hole on the back side oft he LH shock tower at the bottom where the stock return spring can hook. The spring loops into the slot then when you pull back on it, the end of the spring comes through the small hole. Simple with stock manifolds. Not always convieniant with headers. You may need to fabricate a little bracket for the spring. You can bolt it to the frame out of the way.
When I had generic 4-1 headers I had to ball-peen two of the tubes for the z-bar to swing through its arc. I have shorties now but the z-bar is still stock.