I am looking to maybe swap my 2004 2500hd drivetrain into something lighter. I found an 07 shortbed manual. Are the cabs identical? Can I swap everything without cutting, drilling, fabbing? Oh, both are regular cabs. My truck is auto, and the other is manual.

 

The cab should be the same.

Your engine and transmission would swap right in. Things like motor mounts may be different depending on what the engine in the 2007 was/is and the transmission cross member for the 4L80e will needs to be modded because the 2500 frame is different than a 1500 frame.

 

 

I think it would be quite a bit more than 3-400 lbs. Even after swapping my 14 bolt and 80e. My truck is making pretty good power already with 243 heads, cam, turbo, and e85. However its a beat up northern work truck that I don't use for work anymore.

 

 

Pretty sure my 2004 2500hd regular cab long bed and a 1500 regular cab short bed are about 1000 lbs apart.

Dont even know why you are arguing. I want to swap everything in to a cleaner truck.