if i was you i woulndt put nitrous on a car with 140k miles and bad valve seals. if you decide to do it anyway make sure your fuel system is operating correctly/well. you'll want to at least upgrade your fuel pump and get an adjustable fuel pressure regulator. if you plan to stay with the 94-95 intake manifold i'd go for a wet kit. if you plan to upgrade to the 96+ style intake manifold (plastic one) then go with a dry kit.
the reason a lot of people go with a dry kit is because a lot of us are using the plastic intake manifolds. Wet kits tend to back fire if sprayed at to low of an rpm and a nitrous back fire with aplastic manifold isnt pretty. so we use dry for safety reasons. wet kits will give you more horsepower though.
2007 Dodge Ram 1500
2008 Suzuki GSX-R1000
2003 Suzuki GSX-R750
2003 Mustang Cobra 10th Anniversary - 11.2 @ 130
1997 Thunderbird LX 4.6 - 13.7 @ 103
1993 Thunderbird LX 3.8 - Slow
1990 Thunderbird 3.8 - Slower