Before I removed the wheels I tried to shake the cruiser pretty hard and it didn't move.You would be amazed at the size of some of the things I've seen cribbed up on wood blocks in the industrial construction world. I wouldn't be scared of that setup at all. If you don't hear wood splintering as the load comes down on the block, it's fine. Seriously.
I was mostly worried about the vehicle rolling forward since the frame slopes in that location, hence the deliberate wheel chock on the front side of the back tires.