As you know, I've built two 335 clones and a few other "Gibson style" guitars. However I have not built them period correct (and it was my understanding that you are). I do scarf joined heads, stacked heels, change the shape of the head slightly and use a double acting truss rod with a small allen head adjuster (LMII's). (I've also fixed a fair number of broken heads on Gibson style guitars).
I believe that the small allen style adjuster makes a much smaller route into the weak head and I think that a scarfed head is much stronger in that area.
There have been a lot of good discussions on scarfed necks and different truss rods - the important thing to remember is that with that big center block and long tenon you pretty much have to put the adjuster in the head - make it as strong as you can.
The other part of Gibson necks is that they meet the body at an angle (which depends on the amount of arching in your top), they may or may not stand proud of the body, and you've got some interesting fitment at the body. Typically you will set the width at the body joint and pare your neck down to it - remember if you sand the body too much you will thru those beautiful maple plys (ask how I know). Oh, and I know you are building a period correct '50's model, if it has the short tenon make another deviation...,.
ps - I'm sure you've read my rant on other neck threads about thinking about the order of your cuts. Make square sides that can be referenced - you can do almost all of your tenon (with the exceptions of the cheek angle) on a band saw.