It's like comparing apples and turnips. They are two completely different animals. Up until '66 they used a box joint, and the neck was joined to the body at the 22nd fret. Java and I contributed a lot of photos to a neck joint thread over at ETSG before Photobucket decided to keep everyone's photos private unless you paid them.
Here you can see how the box joint is made. It is the full width of the fingerboard. Unlike a mortise and tenon, where the tenon is narrower and gives more surfaces to glue. I think that my box joint was a little longer than Gibson's, as I was trying to get as I was trying to get as much glue in there as I could.
This heel is almost identical to my '61 Reissue. You can see that there is not a whole lot of body structure where the neck is fitted into the body as a result of a box joint.
This is the heel of my '62.
Then, you'll see how the mortise is extended so that the neck could be joined at the 19th fret. I read that this would help prevent so many neck resets. I forget where. But, that was a complaint from dealers, where players complained about how difficult it was to play with the long skinny neck. This was also when they went with the narrow nut, and rounder neck profile.
I don't have a photo of the cavity to show that the tenon is much narrower than the fingerboard on the SG. But it is similar to my Flying V, just not as long. It is quite a short tenon.
