This could be rephrased as
e poi sappiate dire a me
This inversion of the pronoun is common with verbs used in modal form such as volere, dovere, potere, fare and, in this case, sapere. Some examples:
- Non farmi dire quello che davvero penso.
- Ah, poterlo fare!
- Sappimi dire. (the subjunctive/exhortative second person singular is sappia, but in this case the final ‘a’ is dropped)
- Hai innaffiato il prato? Non credevo di doverlo fare.
The last could also be Non credevo di dover farlo, but usually the phonetic clash between ‘r’ and ‘f’ is avoided. Similarly, Bargellini’s sentence could have been
Ora leggete e poi sappiate dirmi se la cosa vi sembri possibile
(current Italian would use sembra, indicative, instead of sembri, subjunctive). The position of the adverb poi is irrelevant: sappiatemi poi dire, poi sappiatemi dire, sappiate poi dirmi, poi sappiate dirmi are all equivalent.