I have almost no SB stuff in my shop, but I do have a 596 head and some stock rocker gear off a 318.
Bolting those crusty old rockers on the 596 head ended up with the pairs having barely .035” between them.
Rockers are 1.665”-ish wide.
Hold down clamps were basically 1.245” and .945”.
The other end of the spectrum I’ve seen are the Mancini/HS BB rockers and hold downs on Ede heads.
Bolt it all on and they’re jammed up solid.
Slightly less than “0” clearance.
