I'm using a rip off/copy 1" 4 hole tapered spacer found on EBay. I like it, alot. I originally used it on my big single plane and now I'm using it on my RPM air-gap copy intake, I spent some time with a carbide bit to smooth the transition from spacer to intake.
Since installing the intake with this spacer under my Mighty Demon 750 annular booster carb. With a more aggressive timing curve. My engine seriously woke up, it starts, idles and revs way better than it ever has in it's entire life.
A short vid of some revs since installing this intake & spacer.
The engine is a roller cam 350, bored .040" over.
Flat top pistons, performance Vortec heads (185cc, 2.02"/1.6") 10.7:1 compression. Comp XR276HR10 roller cam