The REMCO site (they sell lube pumps to make some automatics towable, and at least used to sell driveshaft disconnects) shows 1998 Mustang 6-cyl manual trans "towable as is." Based on that it looks like you can tow in N. I'd add, just make sure the transmission is full to the level plug. I add that to try to help the gears pick up some lubricant and splash it around inside the trans while being towed.
Motorhome Magazine publishes annual lists of those vehicles APPROVED BY BUILDER to be towable. They do NOT list vehicles that people have "gotten away with" towing. I don't know how far their listings go and I'm not a subscriber.
Baseplates are expensive, around say $400. As you price them, check makariosrv.com since when I last looked they were among the lowest and free shipping.