Yesterday, I had a PC issue with the end result being a reformat and new set up on my PC. only about 10% of the way there. But, I saw a you tube video a while back of a very simple and easy mod to make a jig mold accept a swivel.
Although not the video I was looking for, this is an alternate way to make the modification
I had bookmarked a video where the guy made a "U" shaped wire and drilled a hole thru the mold. The swivel was then threaded onto the U shape, and placed in the hole. The u shape was then placed onto the mold face and the legs were into the head cavity. Poured and viola, a head with swivel attached.
I have done the modification a couple different ways and the most critical part of the process is getting the neck area between the swivel and cavity as close to perfect as possible