When i did the 4:10 swap (housings and all) into my sub, it had the quads, the donor didn't. but the flanges on axles end were the same. Vehicle had 4 fairly new shocks, so what the heck! If frame is quad, axle dual, it seems the bolt is the big difference on the lower end.
and.. based on what the donor had, i'd think the rearward shock was the 'factory' mount. Think the 'add on' was more forward/vertical mount' (or at least it seemed on mine...)