I'm sure someone above said , just my two penneth, but I must have read at least 18/- & 6d (92.5p if you're a youngster

) - all good stuff.
Wish I could have better Mondays so I could join in

As suggestion, with no bias or favouritism - why not just the old choose a max per heat per class and let the software do the rest.
Set the same max for the next 4 Mondays and see how that pans out. Should be easier for Race Control as well.
If anyone bawls about being in the lower heat, set up a series, update ability from series results each week and sort heats by Ability.
e.g. if you were to choose 9 as the max
10 TC's book in - bbk will make it 5 & 4
9 Buggy - bbk will make it 1 ht of 9
So you may have 3 heats, or occasionally sometimes 2 and sometimes 4
Late arrivals just get placed where you can.
Anyone driver getting good at this game, going to competitions IS DEFINITELY going to come across slower drivers, so best learn to overtake safely now.
Everyone pays the same money to ride on a dodgem, so why should a 5 yr old get less time than a grandad? (or the other way about for that matter)
just my fourpence hap'nney