I just modified Opticum LTP04H Twin LNB serial No.19-01-0xx
Left F connector for 25MHz reference (Leo Bodnar GPSDO, 8mA drive), right F connector for IF output (no mods).
The original 25MHz crystal left on its place (bottom side), just one track to RDA3567 cut, see photo. So the external reference is now fed via the old crystal.
I soldered the 1nF in ref input because I broke the original C when opening cover. Maybe it can stay as is, I don't know what its value was.
The 49.9 ohm is not necessary, it works also without.