Interesting, I always thought it was done using 1/8th mile to 1/4 mile equivalents. For example. a 5.00 car in the 1/8th (7.9 ish 1/4), will require 7.50 - 8.49 safety requirements and a 5.50 1/8th (8.7 ish) would require 8.50 - 9.99 stuff. work
Only had a cursory glance but I can't find any mention of 1/8th mile chassis requirements in the NHRA rule book shruggy

I believe all the chassis certifications below require a halo or funny car style cage

25.1 SFI Full Body Chassis Spec, Pro Stock . . . . . . . . . . . . . . . 1 year
Adv. E.T. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 years
25.2 SFI Full Body Chassis Spec, 3,200-Pound Maximum . . . . .3 years
25.3 Full-Bodied Car, Tube Chassis Roll Cage
6.50-7.49, 3,600-Pound Maximum. . . . . . . . . . . . . .. . . .3 years
25.4 Full-Bodied Car, Tube Chassis Roll Cage
7.50-8.49, 3,600-Pound Maximum. . . . . . . . . . . . . . . . . .3 years
25.5 Full-Bodied Car, with OEM Frame
7.50-8.49, 3,600-Pound Maximum. . . . . . . . . . . . . . . . . .3 years

'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03