[Jon_G4MDC]

I haven't done anything about FETs. It's not a direction I want to go unless I absolutely have to. I would prefer to match the 455 ceramic filter with passive components if possible.

I think that will probably mean losing the crystal filter or getting involved in a lot of nasty switching to retain it. For all the use it is (unless you are a real CW fiend) I doubt it's worth it.

Presently thinking on how to test the modified filter box. I would like to measure the response before attempting to graft it into a working HRO.
I suppose an oscilloscope might be OK on the 1st IF grid connection. The extra 30pF might have to be lost by a compensating adjustment of the trimmer.

How to drive it at the mixer end of things is what I wonder now. Sig gen + series resistor to "pad it up" perhaps? Ideas very welcome.

The impedance here is critical to get right or the driving impedance presented to the ceramic filter will be wrong. It's the effect of that on passband ripple etc which is the whole point of the measurements after all.