Tom didn't mention it, but for the 21 CMB engine using the NovaRossi step header you have to get a different size silicone rubber seal from Stu (older version part) and possibly bore out the header a little to match it. Another option is to find some high temp silicone tubbing at McMaster Carr. I did that, it was cheap and allowed me to use a stock Nova header with the CMB 21 engine. Just mentioning all this, because if you find a Nova header to fit your 67, you may have to deal with the seal mismatch also.
21 seal material: