You didn't gain nearly 20% in power from a tune on a N/A car... it's impossible. Maybe if 2 cylinders weren't firing and now suddenly are...
Mustangs and all other load holding dynos are superior for tuning, but not for taking reliable, repeatable, and meaningful measures.
Whatever you made stock will remain a mystery (but was probably around 275 - 280 on a dynojet).
Find a dynojet, and you will have numbers that can be more easily compared to other vehicles measured on other dynojets. They are very, very consistent from shop to shop model to model.
Only weather and correction factor choice will obfuscate things -- no correction factor is perfect and treat SAE as a "lower bound" and STD as an "upper bound" on what you will be actually putting down on any given day under those approximate ambient conditions.
Anyway, something in the 295 - 300 ball park is probably close to what you will find on a dynojet with those mods. Perhaps a bit more with nice weather and generous correction factor.
EDIT: Whoops, I didn't realize I had commented on this already some time ago...
