I like Strange Engineering stuff but I'm biased towards the absolute best equipment. That said:
-don't buy your spool if you go that way from one vendor and the axles from someone else as the splines may differ in ever-so-slight ways.
-spools IMO should never be used on the street.
-using you old rear housing may not be the best, smartest or easiest way to go. A brand-new 9" bare housing w/o ends is clean, straight, ready for welding and narrowing, all for reasonable prices these days.