I would not treat with both together. Probably best to finish the current treatment, and then do a water-change before dosing Prazi.
Fluconazole can decrease the metabolism of praziquantel. Also, Prazi puts a considerable strain on the O2 level in the water. In a reef tank, the oxygen requirements are much greater than in a sterile QT, so it would be not advisable to combine with other medications .
What are your plans for adding other fish? Will you be QT’ing other new arrivals?
Since you only have one fish now, might be a good time to remove him and allow the tank run fallow. 76 days would cover mostly everything, including ich/velvet, etc. That way, if you do decide to QT moving forward you are starting with a “blank slate”.
Just my opinion of course ;)