As you can see below, my circuit is mostly the same, important things are marked red and C3 you can try 10uF.
For the parts on original circuit of M49C
https://dl.dropboxusercontent.com/u/43869772/D-M49BC/Build%20Folder%20M49c/M49C%20Schematic.bmp
Don't use R3, C3, R4 - it's low end filtering feedback which isn't needed it's a part of "broadcasting" filter.
You will then get something between first M49 and C version.
C1 use 3.3pF as i mentioned earlier on this thread.
C4 (C2 on my schematic) is usefull feature - it's a feedback capacitor which improves circuit linearity.
After P67 mods - you can try to ad this capacitor in P67 and check how it behave - it's worth to try from 3.3pF - 10pF values.
This capacitor you can solder directly on tube socket pins.
For the parts on original circuit of M49C
https://dl.dropboxusercontent.com/u/43869772/D-M49BC/Build%20Folder%20M49c/M49C%20Schematic.bmp
Don't use R3, C3, R4 - it's low end filtering feedback which isn't needed it's a part of "broadcasting" filter.
You will then get something between first M49 and C version.
C1 use 3.3pF as i mentioned earlier on this thread.
C4 (C2 on my schematic) is usefull feature - it's a feedback capacitor which improves circuit linearity.
After P67 mods - you can try to ad this capacitor in P67 and check how it behave - it's worth to try from 3.3pF - 10pF values.
This capacitor you can solder directly on tube socket pins.