I'm having trouble with the math but I think I am getting close...
You spent $12K for the 3.6 wreck and will pay another $12K for the shop to do the conversion.
Needless to say.. I say go for it, but don't be suprised if the "install estimate" changes before all is done. I also wonder what kind of wreck the car was in to ensure there wasn't damage to the engine/trans to begin with.
for '98's Porsche stiffened the front chassis to handle 18" wheels. 19" wheels weren't "ok'd" by Porsche till the 987 Boxster which again, was substantially revised.
BTW, what happens if another 350Z smokes you..