Hmmm...Having owned several Italian Exotics in he past I remembered a trick.
In the Maserati the trick was to put it in 1st then pull up / over and across then down into reverse.
On the Pantera i noticed that if I slide it into 4th first then it slots into reverse with much more ease.
On these cars many owners have suggested moving the stick into 2nd just prior to shifting into 1st. Can’t remember the reasoning for it, but it does make for a very smooth shift into 1st for me from a stop.
How firm was your clutch pedal when starting to pressing it in? Not firm right when starting to press it in was always a sign to me that my slave had incorrect adjustment or was weak from air in the system (and of course subsequent gear grind).