That looks to be correct, depending on the car. Full body? Stock floors and firewall? Tube chassis? Makes a difference in both sanctions. NHRA starts at a cage being mandatory at 10.99 (6.99) and certification quicker than 10.00 (6.40). The reasons for the rules have been discussed at length, many times.

And by the way, your acquaintance with the Mustang is a moron. He won't be LOL when he cartwheels his flimsy Mustang down the guardrail and gets helicoptered out, if he survives. No rules, no regulations, just fun? Sounds like some Darwin Award nominees. I'll pass. I did tech at a track in the past. I know how stupid people can be. I want a tech guy looking at whatever is beside me.