> I'm using the Lundahl LL1636 trafo on the input: what to do with the R4 and C5 as on the original 312 layout?
This depends on the transformer. Use the R-C network recommended by the transformer maker.
> I'm using a 120Pf Styroflex polarized cap. what direction should the poles follow?
picoFarad caps are almost never polarized. Polarity matters only for electrolytics, which are only used about 1 microFarad and up.
And if "Styro..." means polystyrene, then it isn't polarity sensitive.
If it has a band on one end, that is the Outside Foil. It will work either way, but maybe less stray capacitance if the outside foil goes to the less sensitive side of the cap. If one leg is grounded, outside foil should go to ground. If one side goes to an opamp output, outside should usually go there. But considering the typical size of a 120pF cap, it probably does not matter.