When they are upside down it makes them hard to bleed the air out. It also repositions the shoes. Most of the old articles I've read over the years do it like this link.
https://www.lainefamily.com/ModelAFi...akeUpgrade.htm
It is a bit more work to weld up & redrill the holes plus cutting the notches but I think it's worth the effort. Les Andrews describes it this way in his manual. It solves the spring clearance problem and the rings for backing plate fit/alignment have been available from resto sources for a while now.