There are two types of speaker provisions for the Taurus. If you have the digital climate controls then you have the JBL premium sound system. If not, you just have the normal Ford factory speakers. In both cases, the door speakers are 6"x8" with a separate tweeter mounted by the door mirrors (it's a 2" round cavity).
In the rear deck lid if you have the JBL system you will have two 6x8s along with a mono 6x9 in the middle. If you don't have the JBL then you do not have the rear 6x9.
According to the 1998 Ford Taurus Owner Guide ( 5W-30 )
The 1998 Ford Taurus Owner Guide shows : Motorcraft MERCON - V , automatic transmission fluid For the AX4N and AX4S automatic transaxles
Consult the owners manual for that info.
Motorcraft MERCON automatic transmission fluid ( ATF )
The 2011 Ford Taurus has a 6-speed automatic.
The 2010 Ford Taurus has a 6-speed automatic.
The 2009 Ford Taurus has a 6-speed automatic.
The 2003 Ford Taurus has a 4-speed automatic.
The 2005 Ford Taurus has a 4-speed automatic.
The 2008 Ford Taurus has a 6-speed automatic.
The 2006 Ford Taurus has a 4-speed automatic.
The 2007 Ford Taurus has a 4-speed automatic.