FWIW, per my database, that particular serial number, with a 'R' as the 2nd character, has been reported on Royce Unions. However, this looks a bit better than we typically see from Royce Union. The serial number format may just be that of one of Royce Union's Japanese sources. Best candidate for year is 1976.

I don't think this is a Centurion Semi-Pro. I've seen plenty from this period and they're routinely Miki product with the distinctive wrapover, chromed, stay caps and chromed head lugs.