is it possible to install a grand national motar in to a 2001 comaro with no major problems

a national guard mortar in a 2001 camaro? I think the BATF would have some problems with that!! :)

I know the GN V6 wouldn't fit in 3rd gen Camaros--they had to redesign the heads for the anniversary editions turbo-V6 3rd gen transam. I don't know if the 4th gen has more room or less.

You'd also probably need to do custom headers, turbo plumbing, and wiring. You'd need to make your own engine mounts and crossmember, and have a longer driveshaft made. You might have to notch the cowl and windshield if the intake sticks up too high. None of that is major for a "swap". A major swap is something like this:

http://ls1tech.com/forums/showthread.php?t=730443