Not sure if this classes as unbuilt, but in the recent Su-27 by Gordon and Komissarov book there is also mention of initial plans to fit i believe the Su-27M with the R-79 engine, the one used on the Yak-41. I can't recall now if there's mention of the projected thrust figure, but it must have been at least the 15,500kgf of the R-79V, and quite likely the 17,500kgf or more of later versions with normal nozzle.
On the same subject, perhaps there could be added various D-30F projects, it seem actually this engine started as a project for a 11,500 or 12,000 kgf project to fit the projected Su-17-30 among others, then there were versions to fit the T-10 with several thrust level options (was it the D-30F9?), and the D-30F11 for the FSW S-37 but i don't know for sure what is the thrust of this version, and indeed what are the differences compared to the D-30F6 . Also the other competitors for the AL-31 and RD-33, namely R-53, R-57, R-59 and R-67-300 (7500kgf), the first three ranging from iirc 6600 kgf to 8,200kgf for the R-53 to 12,500 or 13,000 kgf for R-57 and R-59, would be of course be very interesting to learn more about the history of each.