I believe all the rotary joint check style frames were the R or full size, and the FW frames came in after the May 1901 Lewis Patent ejectors-- A friend has a 12 Pigeon Grade made in 1909 (Cody letter) and it has the featherweight frame- smaller barrel lug, and the two additional set screws on the "tongues" of the lockplates.
If you have both a 12 rotary joint check receiver, and a later (up to 1913) std. push rod extractor receiver, both R size- do me a favor and check the dims in the milled out slot in the bottom, where the barrel lug fits- I believe the rotary joint slot will be about 3/32" longer, and about 3/64" wider- which may answer the so-far unasked question here- can I fit a set of extractor Field grade 12 barrels into a receiver 00 grade with the rotary joint design>? My experience tells me- No.
I can also endorse Jerry Andrews- he is a good source for L.C. Smith parts, and is one of the few gunsmiths who can cure problems with a HOT--RWTF