I would get the newer ones as well, just smart as there are replacements if needed.

As for the SB 1420 there were two versions of these, one a bit of lesser quality and had the roller wheel held on with a copper/brass looking pic hit on both sides. The other ones had a removable pin.

I love the older and im my case the 1420-s from the 90-s, 155 on the seat, 455 open and 7500 shifts on a non bushed rocker, cant beat it.

From time to time a single will pop up on ebay and I snag them, but never had to use one yet.