All interesting stuff. i would surmise that if they were "Made in U.S.A." it would say that explicitly.
A little history follows.
Recall during the late 60's early 70's there was the "yellow scare" or "yellow peril" where the western
world thought Japan was going to rule America. This was helped, or hindered, by the likes of people
such as Dr. W. Edwards Deming teaching the Japanese that statistical methods had improved the
quality control in manufacturing resulting in the accuracy of American weapons in WWII (1948 and 1949).
This was presented to the Union of Japanese Science and Engineering (JUSE for short). Men from Bell
Laboratories explained all this to the JUSE members. This was followed by the the Japan Management Association
receiving the training also.
There was a great effort so that Japan in the 1950 would not repeat the mistakes made in America.
Multiple trips to Japan in the 1950s, 1951s, 1952s and education of the Japanese manufacturers,
learning that the customer was the most important component in manufacturing still didn't take hold.
it really wasn't until Dr. Joseph M Juran made his first visit to Japan in 1954 at the request of JUSE,
that the quality started to really catch on. As Dr. Deming explain it, "His masterful teaching gave to
Japanese management new insight into management's responsibility for improvement of quality
and productivity."
"Between 1950 and 1970 JUSE taught statistical methods to 14,700 engineers and thousands of foremen."
So, I would say that most definitely Marantz didn't explicitly say their products were Made in Japan for a time
because of this this scare. Hence the initials S.R.C. then later
"DESIGNED IN U.S.A. PRODUCED IN JAPAN"
W. Edwards Deming, Out of the Crisis, Ninth Printing, (Massachusetts Institute of Technology,
Center for Advanced Engineering Study, Cambridge, Mass. 02139, U.S.A., 1989 [Appendix,
Transformation in Japan] 486-492)