bobthomas1944 you are probably right when you say that it was not build in 1963. But it could have been build the 63 day of 1973.
Murray used a couple different ways of how the date of manufacture was list.
1970's tag format YDDD
1980 and early 1990 tag format DDDY
Late 1990 and Early 2000 tag format YYDDD
Early 2000 on MM/DD/YYYY
Your model number 40702x92c tells us that it has a 40 inch deck was, actual model is 702 and was build for X92C which could be anyone from Walmart to homedepot. Basically it is who it was build for.
You may have better luck by checking the tag or stamping on the engine. Let us know what you find.