[Tom Goldman]

You have to remember the ring is supposed to be stationary in the drum and rotates in the ring land not the drum.
If the unit end play is held to a minimum the actual movement ot the ring within the drum bore is minimal. ...If line pressure is not excessive there should be minimal wear issues with a iron ring. .. I'd use the ATI chrome rings.

I've got several customers with 727's with aluminum drums using ATI chrome rings for years with no wear.
Many more PG'S also with chrome rings , altho ATI now makes their aluminum drum with a steer bore insert to hold up to racers using high line pressures.
I have seen wear caused by teflon rings in iron drums ,and pump ring lands when line pressure is very high. .
Tom