Concrete blocks are fine. Just level them up and place them to match the feet of the tank. The only regs you need to worry about are distance from an occupied structure (25 feet) and keeping it off the ground to avoid rust and corrosion. That's how the propane company would install it.
Check with the propane company as to distance from any structure. If I remember right, Oklahoma goes by an industry safety standard that specifies distance from nearest source of flame based on the size of the tank. Unless it has changed, it is ASME standards. (See link below.) Oklahoma regulations could have changed, so still check with your LPG supplier.
ASME Standards for Placement of LPG Tanks
Oddly enough, even though all sizes could leak, a smaller tank can be set closer to the structure than what a larger one can. If I remember right, a 100 gallon "tank" could be placed as close as 6 feet from the nearest flame source. In our case, it was within the distance to the hot water heater on our RV, which is basically on the outside edge of the RV.