I have a '66 Elco, 454, clutch (previously a Super T-10 and now a TKO-600) and I am running the Hooker SS headers. There are no fitment issues with the clutch linkage, which is the mechanical GM-style linkage... Z-bar style.
Also, my clutch linkage is larger diameter tubing with heim joints, and even so there are no issues of interference with the SS Hookers.
Also, part 2.... I run a McLeod SFI'd scattershield including the block plate, and there are no interference issues with this either (it is larger than a stock bellhousing).
BTW, I first ran the mild steel versions, and when I switched to SS the exhaust bolted up with no misalignment at all. Very nice work, Hooker.
Now for the caveat: If you are running the GMPPD or Edselbrock heads, watch out for the flange on the headers because the lower head bolts interfere and the flange must be clearanced in order to fit flat against the exhaust ports. Word to the wise.
Other than that, if your only worries are clutch linkage interference, then I can say that for me it was green for go... no problem at all.