Ford Mustang: Upgrade 35th anniversary V6 3.8L

I'm very new at this so please keep that in mind. I bought my 1999
mustang conv v6 3.8L with the thought in mind that I would make it my
project car. So far I have put on a dual Borla exhaust system, a MAC
cold air intake, Eibach springs, and 17" racing wheels and tires. Now
this may seem like the stupid part; I could not find a 5 speed 35th
anniversary convertible anywhere. I want to change the engine and
transmission to a 5sp transmission and a very high horsepower engine.
From reading other threads I understand that my next upgrade should be
the gears, but I'm just looking forward to something bigger. Could
someone please tell me what engine is able to drop in this chasis? I
saw a very few SVT Cobra 390 hp engines, but I wanted to know from an
experienced/expert person on what a logical upgrade to the engine
should be. Please keep in mind that I am a real newbie at maintaining
cars and I'm trying to just learn.

Thanks for all of your input guys. I guess I'm just stuck on sticking
to the original body of the 35th anniversary. I know the convertible
is over 4k lbs. and the thought of it ever being a race machine is far
off. I really got into it when I bought a diablo performance chip and
realized the gains I made by doing something so easy was incredible.
It was at this point I realized that I wanted to keep the body and
perform all mods and upgrades by myself. I don't mean to reinstate
too much but before I had taken the computer out and placed this chip,
I was doing good to check the oil on a car. I want so much to learn
mechanics and see what I can do. I think I've done a lot of research
and hard work by putting on my exhaust and dropping it 2" by myself.
I love this car and I really want to stick with it. Knowing myself
and knowing that I won't sell it, wish me luck installing the gears.
I hope to have a picture soon and everyone can tell me what they
think. Thanks for being understanding and not condesending.