Frame question for 66 Chevy truck

I have a 66 Chevy truck that was originally a LWB truck. (with no bed) I also have a 78 SWB frame. I want to convert my truck to SWB and I want to know if it is possible to use the 78 frame. I have measured the width of the frame at the core support mounts as well as both locations of cab mounts and both frames are the same width. So I was thinking of removing the mounts from the 66 Frame and welding them to the 78 frame. My question is this. Has anyone ever attempted this before or seen it done. My only worry is the bend of the frame rails themselves. Althought the width is the same the shape of the frame rail itself as it makes the bends over the front suspension and the dip to go under the cab are not exact but close. Would I be better of trying to shorten the frame I have for a SWB bed or locating a SWB truck for its frame. My reasoning for looking to the 78 frame is I already have it and it is already set up with 5 lug wheels, front disc brakes, and power steering.