Yes the front seats from a 89 mustang v6 will fit in a 91 mustang, the tracks are the same.
Yes.
five
Yes.
Ford Mustang seats can be replaced by taking out all the screws, removing the seat, and placing in a new one.
Yes
2 seats in the front 2 seats in the rear.
The 2008 Ford Mustang has 13.0 cu.ft. of cargo capacity with all of its seats in place.
The 2006 Ford Mustang has 13.1 cu.ft. of cargo capacity with all of its seats in place.
The 2012 Ford Mustang has 13.4 cu.ft. of cargo capacity with all of its seats in place.
The 2007 Ford Mustang has 13.0 cu.ft. of cargo capacity with all of its seats in place.
The 2004 Ford Mustang has 10.9 cu.ft. of cargo capacity with all of its seats in place.