I guess with the SRT-4 Engine, you would almost have your choice of how you mounted the engine. You could do it longitidunal, but then you'd need a transmission that mounted to the back and has the 1/2 shafts come out the sides. LH trans' do this, but they're not rated for much over 250hp. Plus, being automatic, they have a torque converter (which would mean the SRT-4 engine would require a different flywheel).
I think the easiest setup would be to try to cram an SRT-4 engine w/ 5-speed trans. into the intrepid engine bay as a transverse setup. To do this, you would need custom engine/trans mounts, custom shifter linkage, computer reprogramming (if that's possible) and basically a lot of work. I would say to modify the stock internals of the intrepid already, except you still have the trans. weakness problem.