It's a bolt-to-bolt swap...you can use the 6.9l flywheel without any modifications, and the tranny will work just fine, assuming that both trucks are either 4x2 or 4x4 (if one's a 2 wheel drive and the other's a 4x4, there'll be an issue there). You'll probably need to swap the crossmembers, and if the tranny pattern insert for the floor pan is available, I'd go ahead and swap those as well. You'll need to replace the brake/clutch pedal assemblies, and of course any work with the clutch hydraulic system...but, you shouldn't need to do any fabrication or anything on those lines. If both trucks are 2 wheel drive, the yoke for the driveshaft MAY be a different size; if both trucks are the same length (i.e. both are regular cab or both are crew cab), it might be easier to just swap the driveshafts. If both trucks are 4x4, the transfer case will bolt in place with no problem, and no need to worry about the driveshafts unless one tranny's longer than the other (not sure on the length of the C6, but I can tell you that the 4x4 T-19 and ZF5 are the same length).
Hope that helps some...good luck! BTW, welcome aboard!!