Only a handful of A's recieved the letterbox MG port: mostly because of the last in, first out that made up german panzer production.
Steel Road Wheels was introduced: mainly as a material saving method, however, they was scarce as hens teeth as the original version of them had some major issues regarding lifespan. Improved versions was due to enter production and be installed on (in various designs) all Panzers by the end of March 45. In all the factories producing the Panther upon capture, there was still only rubber roadwheels on the line.
While some prototype turrets was produced, its pretty conclusive that none saw combat service: and thats due to there was only one set of the optics for the turret ever being made, and it never left the Ziess factory.
Now, some of the "F" hulls (Again, a modified G hull with the ball MG mount replaced with a ball StG44 mount, sliding roof hatches, and 40mm thick roof armour.) was on line in the DB facility as well as in the early stages at the MAN facility - photo proof of this exists. MAN and DB engineers, when questioned after the war confirmed that no true F's was ever produced, though some of the hulls, as mentioned earlier, may have seen service.
There is no records of true Artillery observation Panthers being built save for a prototype: All the panthers produced by all facilities are accounted for in either issue reports, as well as acceptance documents. While it is possible some was used in the role, they would have been in all likely hood standard Panthers seconded over. The Artillery arm itself, decreed that no panthers would be used by them in order to ensure availability for the Panzer Forces.
Sources: Jentz, Spielberger, Doyle, and copies of German Documents I scored ages ago when I got bit by the panther bug.