Under Hood NHRA Battery Hold Down

Looking for ideas/pictures for a NHRA legal type battery hold down using a group 24 battery and OEM battery trey.
I would like to eliminate the j hooks and the flimsy cross bar. Instead use 3/8 hardware and a nice piece of flat stock. I’m not seeing a clean way
If it’s in stock location ,and it’s tight I don’t think it matters on bolt size , only if relocated does the 3/8 bolt size apply, I may be wrong but the rule book will clarify.