[Jon_G4MDC]

I think there might be another method but it does need the coils to be returned to the original shape more or less.

As helical resonators they must have been almost exactly on the resonant frequency, as they were wound. Just a little high. The effect of an M6 tuning screw entering down the middle of a 30mm diameter coil would be very small.

If the diameter of the tuning screw could be beefed up by a disk or sleeve or some such (inside the box) 146 MHz might be in reach. Tuning stability will suffer however. And I'm not saying about what the effects on the couplings would be.

Somewhere I have a 50 MHz one (originally the lowest design frequency) which I made to tune to 29MHz by adding ceramic trimmers (they were precision beehives - expensive!).