From what I have read, I think that Hichcock header pipe has a removable reducer at the top which matches the port exit diameter to the I.D. of the reducer. I don't know how far into the pipe this reducer goes, but presumably it goes out to somewhere near the first bend.
If it does have this reducer in the beginning of the header pipe, it would be good to use it. It will improve extraction, and thereby improve torque. Removing it and running full open diameter header will make a mismatch of duct diameter too early in the system, and while it may have effect in anti-reversion, it has negative effect on exhaust speed for extraction.
So, if you have the reducer, which I presume that H still includes with that header, I recommend using it.