I came across this low profile bolt on hub adapter. Fits Sparco, Momo, OMP, NRG steering wheel 6 bolt pattern.
It also has what appears to be Grant 3 bolt pattern as well.
https://www.ompamerica.com/en_us/car...ub-bolted.html
https://www.pegasusautoracing.com/pr...sp?RecID=29915
Steering Wheel Hub Patterns | GTSparkplugs
Don't have depth measurements yet but it looks to be at least 1/2 as tall as the Sparco offering.
https://www.summitracing.com/tx/parts/sro-015r98tu