Would you believe Eva that back in 1994 there was a TAFE course here in Canberra that I attended called Horse Race Betting and Selecting. The lecturer was Warren Block, a compatriot of the famous Don Scott. I've still got the original class notes. On the subject of class Warren placed a value of 40kg on a Maiden handicap, increasing the kg rating through all the provincial restricted races right through to Metropolitan OPEN races with a 66kg value. That constituted a massive 15 lengths in improvement. So it would be easy enough to divide that graduation through the ranks up and assign a value. I could email a copy if you wish.
Cheers
RP