Can an Invader be modified to run with a stock SRX? Yes. Aaen pipes, porting, bigger carbs, and clutching can make an Invader really go, but it won't be much fun on the trail. From what I have read, the Invaders limitation is the crankcase volume. It is smaller than that of the SRX. So the SRX has more potential.
Will short tracking an Invader save weight? Yes, if done correctly. Is it worth doing? That is totally up to you. But IMO, no.