As far as where to put the pvc spacer- it HAS to go on top. 1 1/2" > pvc will not set flat on the castellated nut at the bottom of the spring housing. It'll be obvious to anyone who tries it out.
Huh! My memory is failing me. I'm sure I put mine on the bottom. I used a 1 1/2" inline coupler/splice unit that I cut 1/2" off each end. It's probably 1 3/4" od.