Hi Scott,
The 153 Royal had a long run, from 1945 to 1987, and as Ben said, was the bottom of the line model. The fact that it has the shock warning label on it tells me that it's 1970 or newer, and the serial # will give you the month and year it was made.
It should clean up pretty good and since it runs good you'll have a nice machine when you're done. A Royal is like a Timex watch--takes a lickin' and keeps on tickin'!
Jeff
