It is legal, yes. The one in the link I sent you is a heavy duty chassis like yours with the extended spring hangers, so either a military or a 1-ton chassis. In truth there aren't a huge amount of differences in a "standard" chassis and a stage one, just bracketry which can easily be changed from one to the other. If you a competant fabricator/welder making a good chassis up with yours shouldn't be a problem, just takes time!
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