I guess if you want to get technical, the "floorboard" doesn't have to be modded, but you will have to cut a hole for the gear shift lever to stick through. This hole will be in the plate in the floor which is solid with the c6, or if he will let you have it, get the plate out of the donor truck that already has the hole.
The c6 crossmember will not just "move back" and drill some holes. The lower part will, and the c6 mount will work also, so if you are alright with just using the lower crossmember, than that's it. Letting the tranny and the crossmember just sit on the lower lip of the frame was not good enough for the factory, and not good enough for me either. When you slide the lower crossmember back(the holes in the lower lip are already there) then the short upper crossmember braces will not fit. If you can get them, get the short upper crossmember pieces from the zf truck. Then everything bolts in, no drilling. You could try to redrill new holes for the old c6 upper crossmember pieces, but unless you had a small 90 degree drill, I don't know how you would get in there to do it.
You definitely need the pedal assembly. No getting around that. And you have to take the whole dash apart to do it, since the speedo cable goes right through the hole in the assembly, so the cable has to be taken loose and pulled down to get it out. I also had to drop the steering column from the dash, and push it to the side as far as I could to fish the pedal assembly down and out. My truck had a block off plate for the clutch master cylinder mounting. Take that off, and the master just bolts in, no drilling.
The wiring harness you need starts under the brake booster. On my truck is was a lime green plug. It then runs down under the truck and plugs into the tranny and the transfer case. There is a metal loop on top of the frame that holds this harness, that takes more time to get loose.
Get the zf rear driveshaft, and also take the big nut loose on the rearend and get the yoke. The zf driveshaft is shorter, has bigger u-joints, and is twice as heavy as the c6 driveshaft. You need the yoke out of the rearend so the bigger u-joints will fit.
Don't figure on using the original flywheel. You can check it out, but it's probably wore out. It has moving parts and wears just like the clutch. I have heard over 5/8 movement is no good, but the used one I got had several of the plastic pieces missing in it. I took the original flywheel apart and bolted it together, and put a new clutch in, but it's noisy.
Was it worth it? Yes. The c6 is a tough tranny, but the torque convertor they used is too loose for the diesel engine.
