Well...
Every creature has a level with a leter after it. The letter is level variable, and their is a table that can be rolled on to increase or decrease or leave the same a creatures level. Looking at the table, you will see there is a max number of levels a creature can gain. I have always used this as a guide for maximum level of a creature.
Every creature has hits, and behind the hits is a letter...this letter can be referenced on a table and hits gained per level of exp over base can be found, depending on creatures Co. I always assumed 55 for most creatures, 90 for tough ones.
For every level over base level, OB is increased by 5.
Etc, etc. These rules fill the first several pages of Creatures and Treasures and C&M.
lynn