Single Point Jack Plates, Low Profile Jack, or 2X6 pine (4).
My 240 oil pan sits lower than the crossmember and I can get a Harbor Freight $100 jack under the TC box and diff. I run 16/8/245 all around on a lowered car.
I run RA1s on the race car since we can't run slicks in my Group which are 225/25/15(F & R) and and here's a picture at full droop (running with slicks during an HPDE - 225/45/15 -F & 275/35/15- R)
Fixed measurement points (center of fender inner lip, rocker, TC rod box, crossmember, diff) would allow us to compare car to car.