[Radio Wrangler]

The purpose of that transformer in the circuit in which it is shown iis to make opposite phase drives for the crystal lattice pair (Half-lattice if being precise)

If you went to a ceramic filter, the transformer could do some impedance transformation if that helps, considering the exact filter chosen.
These ceramic filters are piezo-acoustic devices driven by the voltage applied to a pair of electrodes. They are essentially balanced, but are usually applied unbalanced. If the filter has connectivity from input to output ot to case fro one input pin, then you can't drive it balanced despite the elements involved inside it being so.

The selectivity from the extra IF resonator may still be beneficial.

There is no right or wrong, just a lot of little compromises. It's a maze to be navigated were you want to lose least in the parameters you most value.

I may be mis-understanding the goal, which I think is to get a narrow filter suited a little more to SSB at the cost of less suitability for CW.

If you want a serious 6 or 8 pole SSB filter, Ive probably got a spare one you can have. Impedance will likely be 50 or 200 Ohms, so you'd have to do some transforming. The snag is they are quite big.

David