It sure looks nice and original and it would be a shame to switch out the original parts. I have a 1987 Miyata 1000 and I wish I could have kept it original. The differences between the 610 and the 1000 are minimal with the 610 having a different fork and rear stays - take a look at the old catalogues. (Insert drooling smiliey face)
Gordon p
http://www.miyatacatalogs.com/2007/1...alog-1983.html
http://www.miyatacatalogs.com/