My 91 didnt' have one either. Seem to recall that only the new heads ('01-) have the bleed screw installed on them. My '03 does. There are techniques posted here that explain how to bleed the coolant in the older bikes (I never did with my 350, just let the thing run for a bit with the cap off), never had an issue, and my radiator had 10% of itself removed.
-Parsko