I have been installing cylinders like many of you. It would be nice to own a set of piston base holders but the buy in is pretty high...the lowest I have seen was $40 each; that's $160 a set for a piece of machined aluminum.
Every now and then a couple of neurons fire together. This recently happened when I was looking at some Delrin blocks. So I had a set machined .......cost $40 for a set of 4.
If interested I can post the machinist e-mail address.

When given the choice between being right or being kind; choose kindness. W. Dyer