I'm not sure what aspects of the question are important, and it's lacking some details, but here goes:
50 years ago? That was pre-1997 rewrite of Part 61. Unless the rules had changed again earlier than 1997 in this regard, at that time "solo" time (such as student solo) was NOT considered PIC time.
So, if you were signed off for solo in the Aztec Nomad seaplane, and flew it solo, you could not log it as PIC.
If you were NOT signed off for solo, for example you were an AMEL (no sea) plane pilot and the owner asked you to reposition the aircraft, then at least today you could not make that flight legally. If you did, then you wouldn't be able to log anything anyway.
If the airplane is amphibious, and you only land on land (not water), then you could legally do the flight with an AMEL certificate.