The limit is 75V but there is a table in the rules that tells you the limit of each type of battery.
So you can only use a max of...

30 NiCd cells, 30 NiMH cells, 18 SLA cell's, 12 LiFePo4 cells or 12 Lipo cells.

So the limit may be 75 but even with a lipo at maximum voltage you will only reach 42V anyway.