I don't have the Honda lower spring keeper / seat or fox lower spring keeper / seat as they are installed on my Pioneer at the moment.
Just wanted to show you how I made the bushing using a 1-1/2" black iron pipe nipple, a machine shop no doubt could make the same part and look a lot nicer but I like doing things myself when possible.
You'll notice that I keep using the same words over and over, this is to make it easier for someone trying to figure this out from the beginning with little to no knowledge about suspension parts.
First, a reference picture for the parts about to be discussed. Red arrow is pointing to the Honda OEM lower spring keeper / seat. Blue arrow is pointing to the Fox spring keeper lip / seat.
First cut needs to be on the threads as this bevel fits snug inside the Honda lower spring keeper. The bevel of the threads ensures that the bushing cannot slip through the Honda lower spring keeper, stays nice and snug.
Second cut is off of the threads on the flat part of the nipple cut to the depth of the Fox lower spring keeper lip minus the Honda spring keeper.
I then grinded the flat portion to a slight bevel until the bushing & O-ring "coming up later" would fit perfectly inside of the Fox lower spring keeper lip/seat.
Smoothed up the threads for no real reason to be honest, don't go crazy here as it needs to fit snug inside the bottom of the Honda shock keeper.
Add the O-ring and done. I primed and painted mine before installing them for rust resistance over time.
Red arrow portion goes into the bottom of the Honda lower shock keeper, blue arrow with O-ring fits snug inside the lip of the Fox lower spring keeper. You may have to go back and forth to the grinder until the o-ring fits nicely inside the Fox spring keeper / seat. Used the o-ring to eliminate any side to side movement where the two parts meet.
Not the prettiest part ever made but it works exactly as intended.
Last picture shows where the bushing is in relation to the other parts. Don't make fun of my windows paint skills!
Here's a non marked up picture for reference. Tire is flexed out in this pick if you're wondering why there is no shock shaft is visible.
And there you have it, a little redneck engineering. Improvise. Adapt, Overcome.