Clarification and Measurement re: 1969 Barracuda Backup Lights

I just took the dog for walk with my wife and wondered the same thing about whether reverse lights are even a legal requirement. Is so, I'll look into alternatives as well. Also occurred to me that the crossmember you referred to is not likely drilled open either, as it is a '68 car. So many unplanned moving parts in this project ... many thanks for your input !
In all the years that I've been driving and going through inspections, I never recall anyone checking reverse lights. Good luck.