This would be different?

[dabears]

So i see this setup all the time but i dont know what its called? i think it would be cool to do with a couple of rollers and a working truck. Can someone tell me what this set up is properly called i cant find nothing on google and this is one of like 4 pics i could get that are of this. More so im looking for more pics of the frame mount for them. I know its 4x4's and 2x4's but how does it attach to the underframe?? thanks for the help heres the setup!