Chuck, all of the 20 gauge guns that have been observed with the "R" suffix have been guns with the Curtis forarm. It was a push button on the end of the for-end almost like the release on an Anson-Deeley for-end gun. These were used from sometime in 1912 to sometime in 1920. They were put on all L.C. Smith's that did not have ejectors and it was to stop the for-end from falling off and getting lost in the field. A very time consuming part to make.
The "R" prefix is denoting that the gun is on a Regular frame.
Also as Dick stated, please renew, now it can be done on-line through PayPal.