Getting to 250 isn't hard, in fact getting to 400 hp isn't that hard, it all depends on your goals and your budget.nsaikia said:
the fastest way would be to simply supercharge with a centrifugal SC, and you're going to 275 hp with no real consequences to powertrain, etc, unless you spend a LOT of time over 3000 RPM. The boost isn't high enough to damage anything until that point in your powerband. However, even at 3000 RPM, with the intercooler, you may shorten the life of the engine by 15%, but running at that high an RPM will shorten the longevity by around 10% anyway.
The 7.5 on the 2001+ cars use the same axles as the GT's, and will take up to 350 hp without much protest.
Suspension needs will be determined by how you go about modifying your car. with a centrifugal SC, you won't need much, with a Roots SC, because the boost comes on at low RPMS. Engine life will definitely be shortened with a Roots blower.
So, in short, you have the 1st thing (a goal). you really need to decide what your budget is, and your driveability requirements. Do you want to go naturally aspirated? You CAN get to 250+ naturally aspirated. Is it a small budget? go N2O. Do you want good MPGs? Go N2O or centrifugal SC. DO you want a torquey engine? Naturally Aspirated+gears or Roots SC.