When I dropped the V8 into my Mustang, I actually used a non-HO motor like what you have in the town car...

Yea, the same bolt-ons will work. There is a slight problem though...the crown vic motor is speed density with 14 lb injectors. If you start doing much of anything to it, you're going to have to swap to a mustang computer and at least 19 lb injectors. If you do that, you'll have to swap cams because the firing orders are different. If you're serious about doing this, I've got a stock HO cam and fuel rail w/injectors I'll let go real cheap since it's just taking up space around here. I think I may also have a speed density computer out of an HO motor laying around here somewhere as well.

The first thing I'd do is slap a set of HO heads and an HO cam on the car as those are the biggest restrictions you've got right now.