Your fenderwells are a special situation. Most FW (cough cough hookers) are WAY too long and if shortened/sized better there big gains changing from the hooker FW variants.
These were under chassis SB headers and they aren't making that difference.
Yeah, I went to tti under chassis from the fw hookers.
The sb tti headers you mentioned, lost power on the last engine vs 1.75 hookers, somewhere around 30 hp.