Another quick ? About the 1970 axle widths

[Hawssie]

I read here that 1970 was a transitional year regarding rear axle widths concerning the 2wd half tons. With some early 1970 trucks having the 55.5 width and the later year models having the 57" width when measuring B.P. to B.P.. I also read that the reason GM widened the rear was to match the increased width of the front when they brought out disc brakes in 1971. I then read one concern with converting to the wider width axle on an early truck would be a miss matched front to rear width. Meaning that if you sourced a 1971 up rear end you would end up having a wider rear width then the front. My question is what happens when you convert to disc brakes on a 67-70? I bet everyone doing the 6 to 5 lug is also doing the drum disc as well. Does this brake conversion also increase the width in the front and now equal the newer 71-72 width? Or is it somehow still the same width as before when it had drums? It seems that if it is the disc brakes that makes front wider then it would actually be a truer match if you converted to the wider width 71 up rear axle and really not a match if you got the Brothers early style conversion and kept it narrow. Also if this is true then it seems 1970 trucks with the wider 57" axle would have a miss match front to rear width from the factory. Also what are the advantages of going to 5 lug in the first place, is it really just the wheel choices available?