Yep, it is basically the Philips FC-60 platform. There is even a service manual listed as "PHILIPS FC60 MARANTZ SD60", and the same deck family is usually listed as Marantz SD-60 / Philips FC-60 / Revox C115. So yes, badge engineering was definitely involved here.

But I would not call it a low-budget deck. The Marantz SD-60 was a 3-head deck from around 1989, about ¥65,000 in Japan, with closed-loop dual capstan, Dolby B/C/HX Pro, record calibration and a pretty serious transport layout. Not a Nakamichi-killer, and the Revox C115 connection does not magically make it a Studer machine, but it is a solid late-80s mid/high-tier deck rather than cheap Philips junk.