77 cb750k head pipes with hollow reverse cones from eBay. I have some 1-1/2” perforated pipe to baffle them a bit.
I started putting this together when I was going to race my cB750 in the production heavyweight class, which requires a 4-4.
Instead I race my 400f in production lightweight and bump up into heavyweight… the 400f does just fine in both classes.
If I ever get this bike back together I think I’m still going to run these.