According to one site
I found, PTJ is the manufacturer's code for American Radhial.
A trademark page
says the company name Radhial was filed for by an Italian boat manufacturer, Plasteco Milano. Looks like they originally had the shop in New York, and one in Anchorage, Alaska. The one in Alaska is pout of business; the NY shop apparently ended up in Pembroke Pines, Florida, possibly bought out by Nautica, but I can find no further info on their new location.)
I suspect that the boat was bought by AR as an OEM tender for a cabin boat (which Nautica is reported to have built.)
00505 looks like the serial number, 88 could likely be the year (trademark filing was in '85, as I recall); no idea what the G 7 is.
Hope this helps;
Sorry; should add that anything not on one of the webpages is speculation.