13 years ago or so there was a manifold / header test in 5.0 or MM&FF mag.
Car Craft have made a similar headers comparing test just using a mild 350 SBC. Some not knowing how headers actually work will be surprised that the mid length shorty headers (JBA style) in that test made about 20 more peak hp (at 5500 rpm) than the long tubes with same tube size. But the shortys was down on power below 4000 rpm.
In the tri-y vs longtube test, the tri-y was down on hp up to 3500rpm, and made 20 hp more 4-5000 and similar hp from 5-6000 rpm.
They also tested 1 5/8 vs 1 7/8 longtubs on a hot 406". The big tubes first started showing hp gain above 5500 rpm and under 5000 they made a noticeably loss.