[Finster]

Looks good so far. I have a suggestion which I don't know if it would be an improvement or not, but here goes: Since you mentioned it's difficult drilling the delrin deep. How about instead you use a tube (brass/Al perhaps) and fix a nut (glue/weld/braze/pin) on the end inside to match your threaded rod. No deep drilling required and if you need more throw just lengthen the tubing and threaded rod.