well if you watn to keep that car dont do a 4.6 swap... to a 5.0 swap much easier cheaper adn faster. just buy a 5.0 motor and rebuild it with forged internals or at least forged pistons adn good rods. then put on a nice set of heads, i would do AFR's and then upper and lower intake you want wtih a cam set up with the heads and intakes for best performance, finish it off with headers and bolt ons and get it ready to go in the car by geting a computer and wiring harness along with a new K member and the right motor mounts and if you have a T-5 just get a bellhousing for it and new cltuch you should be able to do all that for 5 grand EASY adn you will be pushign 300rwhp adn tq maybe more.
you could alwasy buy a notch back 5.0 mustang and rebuild it/paint it restore it what not dotn buy a hatch back they are EVERYWHERE adn dont look nearly as good as a notch back.
you could finally just buy a gt or cobra and be done with it for the most part after selling your car, you should have 8-9 grand