Glad to participate, and thank you for your efforts, Doug. Here are 3 Izzies that are within reach, I can post some Tulas later. Should be useful data.
1. 1963 Izhevsk, ВЯ5512, T-C Д10, Euro de-act that includes a lightened/matching rear sight; source unknown
2. 1971 Izhevsk, EЗ4313, T-C H6, PLO AKM front end that includes a cast RSB; private seller
3. 1975 (late, 22mm) Izhevsk, 419455, T-C Ф1, PLO AKM front end that includes a milled RSB; private seller