Rene,
Actually the PC7 is quite well documented. Google "Some ideas on racing seaplanes" or "NACA-TM-691" and you should find a pdf file of an article written by Pegna and translated for NACA. There is also a pdf of the original Italian version out there too, "Alcune idee sugli idrovolanti da corsa". The general arrangement drawings in this article are slightly different from the final aircraft, but only in small details.
Regards
Ralph