V-6 auto?? Yuck.
I undertsand your want for an upgrade but that's gonna kill that car. If you want to update the drivetrain go with a 2.0 or 2.3 Ford 4 banger and a 5 speed. They are widely available, reliable, respond well to performance upgrades and are highly supported by the aftermarket. Not only that, but they fit very well in the smaller engine bay and don't look that out of place in a car such as yours. It is actually a pretty popular swap. Lots of info out there on it if you do some digging...
Here's a few in different stages of dress -