if you are getting one this year, then yeck, you only have a few days left to get it, so why bother with modding the one you already have?
but i bet you really mean you are getting a new one either in 2011 or 2012 ...
to get to 400 out of one our motors while not touching the bottom end, you are talking about a blower and better heads aind intake.
a very well executed naturally aspirated heads/cam/intake combination on a 331 or 347 stroker motor can also net about 400 at the crank, or even maybe 400 at the wheels.
for that, you are looking at probably 3-4 grand.
mind if i ask how old you are? for me, 2 years is not a long time any more because i'm 50, so 2 years is only 4% of my life.
it is my opinion that getting into all that for the short run (with the plan of replacing it pretty soon anyways) is not worth the cost. you never get what you put into if back. i would just double down on the savings and make the new car happen sooner. otherwise, you are just throwing money away.
now if you decide to spend the 3-4 grand for more power anyways, then consider this option ... sell your car and take the money you get for it and add 4 grand to it and make me an offer for my mustang. i am selling it to finish the fairlane in my signature.