Hi there. Over time, some members have done simple google searches on this information. Here is a link of things to try:
http://www.mypianofriends.com/links-for-piano-serial-
number/dates-99.html
A member from BlueBook offers this:
http://www.bluebookofpianos.com/grades.html
I'm a little confused about your final question - you have the piano in your possession but wish to know about it's quality and sound? Generally speaking, Yamaha make excellent pianos - sound build, sparkling treble, bright bass.
Trust this helps.