Ground clearance/drop question

[RockHQ]

Okay here's the deal. Our government mandates a minimum of 8 CM, or 3.15 inches of ground clearance for all vehicles, this measurement is taken from the lowest point of a vehicle's chassis, or any integral part of the vehicle underbody.
Now since i'll be lowering my 79 C-10, i'd need to know just how low i really can go and still be street legal.

I'd really appreciate if someone with a 3/5 or 4/6 drop (or more)could measure the distance between ground and the lowest part of the frame/suspension, whatever is the lowest point?

Right now i'm thinking of running 15x8 wheels with 255/60/15 front & 275/60/15 rear. Hopefully i can get away with a 4/6 drop, but if not something else will have to do.

Thanks,

-Axle