I don't know if the struts on my 2010 2551 are factory or not. There is one at each end, 60# 16" long. They work fine with the 2" memory foam (heavy material) we added under the factory mattress, but are way too strong without the memory foam. In fact, the bed is hard to make and pops up on it's own without the heavy mattress pad. I would bet two 40's would do the job.
PS I'd have put the block on straight...