highest time a slant six can do?

HI:
Google "Super Six" and you will find sites that discuss converting your one barrel to a two barrel. You will need a carb, intake, exhaust, and throttle and trans linkage set up from a Volare or Aspen slant six from the mid 70' to the early 80's. It' is all pretty much a bolt on rig.
Also you will need a slightly larger exhaust pipe from the manifold.
Also check out shaving your head a bit to increase your compression.
Check it out!