This is the first time I've heard of using a 2x4 block just above the bogey box casting. Trying to get my head around the forces involved.

It seems to me that the ~2000# wheel load acting on the ~18" horizontal bogey arm lever would potentially crush the end of the 2x4 which has to counteract that same load but using a much shorter (maybe ~6"?) lever arm along the vertical bogey arm. That would put the load on the 2x4 very close to the ultimate crushing strength, of say Doug-Fir, parallel to the grain. The curved bogey arm wouldn't present much bearing area initially, but would compress and potentially start cracking along the grain.

Again, first time hearing about this and I have no experience with it and Jim K does. Anyone else use the word block above the bogey box?

If there's no danger of the wood crushing and splitting it certainly would be the fastest way to relieve pressure on the airbags. Blocking under the bogey boxes and relieving pressure on the airbags takes more time, but takes pressure off of both the airbags and tires.

Richard