Welcome aboard, this link will explain the 1968 VIN number scheme.
Basically, if the the first three digits are "242" you got a goat.
http://www.gtoalley.com/sixeight.html
If you send your VIN number to PHS (Pontiac Historic Society)
http://www.phs-online.com/ (along with $35), you'll get a copy of the actual build sheet for your car detailing all the options that were originally ordered.
The 2-letter engine code is located on the passenger side front, just under the head, below that should be a 5 or 6 digit number that would match the last 5 or 6 numbers in the VIN (if it's numbers matching).
There is a wealth of information at
www.wallaceracing.com as well.
Seeing that you are in Texas, you are out of the rust belt, so a local car should be good (rust wise).
Good luck and post some pics of the GN, Any GM car (except chebbies) are accepted rather well here.
jamie