Need advice on which car to mod..

Here's the delima. I've got a child on the way and one of the cars have to go - between a 98 Corvette or 96 Cobra. Both cars are starting to get boring so it's time to modify but boss says one has to go. The Vette would make more financial sense to sell, however the LS1 is a great motor to build. I can get in the upper 500 horsepower range with a supercharger / heads / cam. But I'm looking for what can be done to the 4.6L 4V to get the same results for the same money and I'm not finding much luck. It seems that the old pushrod 5.0 is the modifiers engine of choice. So what can I do to this motor to get into the 550 - 600 hp range? And would this include a built bottom end (which will ultimately cost more than what I could do to an LS1 to get the same power)?

Thanks for your advice...