Ok, I decided to devote a little time to discovering what I could about the Shinko Musical Company.
So far, not much has turned up but I did find a couple of teasers.
First, here is a description of the Shinko company that appears in a 1968 edition of Japan Music Trades. Not much info other than the company was located in Nagoya which is the major industrial port city in Aichee prefecture and one of Japan's long established guitar making centers. Nardan guitars are acoustics; no mention of Pleasant.
Another teaser comes from an ad in the same issue of JMT. My question is what do these companies have in common so that they would appear in the same ad? My first idea was that they were all based in Nagoya but that is not the case. Two companies I recognize, Zen On and Kokusai are both from Osaka.
Maybe we can persuade sneakypete to drag his wife over to the computer screen and give us some idea of what the text of this ad says
I do know that Kokusai was founded shortly after the war and distributed instruments from Hohner and Wurlitzer.