Racing Head Service (RHS), used to offer a large port SBF, 20 degree cylinder head under their ProAction line. These were based on an Australian made cylinder head.
They were available with 185cc, 200cc, 215cc, 221cc and 235cc intake ports with chambers in different sizes, as low as 58cc. There still some out there for sale and they pop up in Ebay all the time. I have a new set of of the 235cc bare castings and would be a head to get approved as an alternate to the N351 head.
https://www.speedwaymotors.com/RHS-3...cc,225808.html