spiral balance sizing question

I recently purchased 2 29" 600 series spiral balances. The old ones measured out at 5/8". They were the Alcoa balances with the white plastic coating. The new series 600 balances were very difficult to get into the slot on the side jambs. I was able to get them in with a little more force than anticipated. I wasn't sure how snug it should have been. After I attached the balance and opened the window the tilt release latch was rubbing against the metal tube and making a screeching noise.
I know the metal tube is more rigid than the plastic but I wasn't sure if the 900 series would also work and give more clearance between the latch and rod.

Also on one of the jambs, the slot where the screw plug inserts was broken and missing a portion of the plastic which doesn't allow for a snug fit. In fact the plug actually fell into the slot and dropped behind the jamb. Is there a plate that's available to cover the slot with the correct size hole to receive the plug and cover the missing area. Or is there another repair option. I thought maybe some type of epoxy to repair the missing piece that would allow for a snug fit might also work. Any suggestions