The stock bottom end can handle about 400hp as long as it is tuned properly and you dont go all boost to make that number.
For the weight that you dropped you can expect .300 seconds faster. For every 100lbs shed or gained it equals 1/10th of a second. So dropping 500lbs means half a second faster. Easy Math.
Now for your Sixers power, first off I strongly suggest going over to www.SuperSixMotorsports.com
and talking to the owner (Tom) over there, he can set you up with everything you need if you tell him what you are looking for an have the cash to flash.
You have a splitport 3.8L even fire V6 which is far better than the old single port version of 98' and older. Think of it as having a double intake really, one for torque and one for topend.
Anyways, your heads cant be ported as far as a singleport but they flow better and have a refined water passage system and are less likly to crack and blow head gaskets than the 98' and older singleports.
Your car starts out strong with 190hp.
I will list your mods next and give a generalized hp number, but be warned, most of the numbers are more accurate for a V8 than a V6 especially when it comes to improving flow numbers with a CAI or TB or headers or exhaust. So you could probably even bet less than, also this is engine horsepower not wheel horsepower.
BBK CAI= About 10hp (Better throttle response, nice whistle)
BBK UD = About 10hp (Quicker revs, better fuel economy)
H and catback =about 15hp (possible loss of torque, note change)
El Diablo! =about 15hp (Better tb response,better economy)
BONUS!!! = 5hp (Uprages together compliment eachother)
So generally saying you are going to see about 245hp out of your engine, the companies would like to make you think that there is even more than that, Diablo claims upwards of 30hp in many cases but doesnt note much of the applications such as engines already producing 300+hp
The suspension upgrades that you have will undoubtadly increase your 60ft times, more power is getting to the ground and thus better launches. The gears that you are running are great for the combo but for as how fast you are in the 1/4 mi, I cant tell you for sure, I dont know how you drive, what the conditions are or what track you are using. More than the car comes into play.
I think you should stop playing around and get a set of long tube headers, a SSX sheetmetal intake from Supersix and a set of their most extreem heads and stix along with a 75mm tb, 38lbs injectors and have it dynotuned properly. That will get you into the 300hp zone, along with how light the car is already plus your subtractions I think you will be very happy with that.
If you arent and you are a true Sixer Fan then have SuperSix make you a 4.3L shortblock and shoot over 400hp w/o a power adder.
They are dipping into 600hp land and higher now with Forced Induction engines and even higher with Nitrous mix.
There arent many Sixer guys around and info is sometimes hard to find, the V8 guys (Though they may mean well) dont really understand the differences between the engines and like to say (It cant, you wont) quite often, so check out SuperSix and get all the help you need over there.
Personally, I would go with a dohcV8 swap
The V6 is going to cost you more in the long run than say a 03/04 Cobra conversion.
Good Luck with everything.