Which is better, the caliper on the trailing side or the leading side? Why so some companies switch it around?

 

can I move the caliper on a 9-bolt if I move the backing plate around? I know I would have to change the lines

 

When I did my rearend swap from drum axle to disc, I pondered with the same problem. Nothing made sense to me as to why one caliper lead and the other trailed. I questioned if possibly GM used the same axle/brake combo in another vehicle and it was just mass produced that way for a universal fit into other cars that had clearence problems with the RR caliper on the trailing edge---I came up with nothing and am still puzzled.

Anyway, I decided to leave it alone because I figured that GM engineered it that way for some specific reason otherwise they would have put it on the back side like the other (and all the replacement parts fix to it that way like you said).