[alffie]

Depends on what your definition of interchangeable is. They use the same mounts,clutch,bellhousing,alternater,pullys,you can use a LS2 sump if you want to wet sump them. The harmonic balancer is differnt but the cams the same (differnt grind) timing chain the same. The differences are dry sump set up, block has 4.125 bores, heads have 2.2I 1.64E valves.
Get a LS7 while your over there you can pick one up for $US12000, you will never look back. See if you can get the LS9 that would be a good motor.