Gidday!!
Try messing with ceramic resonators instead of quartz.. These can be pulled very easily. My FRG7 has a few Cmos gates as the oscillator feeding the existing emitter follower into the product detector, works very well. It is not unusual for these older IF filters to have odd cFs. A few other mods help enormously with front end performance with these radios.... a more "normal" balanced mixer in the front end, and another at the second mixer. Doing this helps the cross mod, reduces noise quite dramatically. Also AGC the first IF amp, gain here is fixed, and much too high, also remove the source bypass cap. Increase the 2nd IF gain by removing the damping Rs across IF primaries, and short/remove the unbypassed emitter resistors. The transformers will now peak quite sharply, gain will increase. A voltage doubler AM detector too helps weaker signals in this mode. If running on mains, the regulator can be fiddled to supply a higher voltage to the signal circuits... helps dynamic range..... There are also mods to the Wadley loop to increase oscillator injection purity. This was implimented not very successfully in the FRG7000, the next and last model to use this system, but if you check out the 7000 schematic, you will see the differences. These sets perform bloody great!!