We tried Passiflora manicata and one or two other pink-flowered or red-flowered species, from highish altitudes, in the open ground in a fairly shady area of our hot Greek garden, irrigated twice weekly during summer. They did not survive, defeated by the dry heat.
We have never seen any of the red-flowered or pink-flowered passion flowers flourishing in this part of Greece, and suspect that in Rome you have set yourself a tremendous challenge, David! I do wish we could grow them here, so if you hit on the magic formula that will be terrific. It sounds from your experience as if it might be worth our trying Lady Margaret, though....