these made great low end power, the ones in photo have a 30 inch runners in side, peak tq of 495 came in at 2800 rpms and 375 hp. they made a 15 inch inside runner too that look almost the same on the outside but peak tq of 485 came in at 3600 rpms. and peak hp 390. as a kid reading about these set ups always thought they were great and still do lol
I have thought about the intake spacers as a way of using other nailhead intakes instead of trying to find a 364 one.
They only work on 6x2 intakes at that thickness. You can get a slight power increase with a thinner riser only due to the decrease in manifold temps. I dyno tested them about 20 years ago