Well, it's easier to help you since you have a goal for your car
The easiest way would be to sell the v6 and buy a v8, but if that's entirely out of the question, there are many different routes you can go.
The quickest way to keep up with the chevelle while keeping the v6 would be a power adder ~ supercharger, turbo, nitrous
and a well built engine. Do realize you have to beef up the suspension, drivetrain, and possibly some engine internals to handle the extra load. This can get costly considering just the supercharger/turbo usually costs around $3500-5000.
You could do the v8 swap as stated above. I would look for a 4v as darkshadows said. It is leaps ahead of the GT's 2v, and has more hp: 99/01 ~ 300-320, 03/04 termi ~ 390
Though if you had to, the GT v8 would still be better than the v6. A donor car would make the swap easier. If you're not a manual already, you may want to consider that as well.
Doing the v8 swap is probably the more sensible route, since your dad is a mechanic, you won't have to worry about labor costs. Plus spending 5k+ on a supercharger for the v6 will only get you up to where the v8's start performance-wise, as to where you get the v8, it only gets better from there once you start modding.