Well, It's not that hard, but you have to be careful. What I did was make a template of the heel, then transferred it to the body. I then traced the template and routed. You don't have to take out much, just round the corners. Also, the pocket was slightly narrower than the heel. I tried to take a little bit off the side.
I WOULD NEVER EVER DO THIS AGAIN! IT DID NOT TURN OUT THE WAY I WANTED!!!
Next time I would just sand it wider until the neck fit. The old router is an aggressive power tool!
But, consider I paid 40 for the Epi, 60 for the neck, it wasn't too much money to learn on. And, it's actually turned out to be a great player, and I get a lot of compliments on the look and sound (DiMarzios helped).