Thanks Unicornst! 

I increased the size of the head a bit and moved it around until the edges matched up as close as possible with the edges of M3's neck.  There was still a tiny gap under the jaw that I couldn't match up, so I took care it with postwork... the 'Push' and 'Soften' brushes in PSP8. 

"You don't know what we can see
Why don't you tell your dreams to me
Fantasy will set you free." - Steppenwolf