Probably separate pieces. If anyone has a fiber optic camera that Dave can borrow... No idea about these but I am working on getting answers.
Working on some more info I’m on the mold...in the meantime here is the link to the original auction. The seller did have another mold at the time but I do not know how to search past auctions. https://page.auctions.yahoo.co.jp/jp/auction/j637049672
I got in touch with Michi at M1GO, she confirmed that the factory went bankrupt, and the mold was never returned. We haven't connected the dots between the bankrupt factory and the YJA seller yet but we may never solve that part of the mystery. Yuji made a post about it on Facebook: https://www.facebook.com/photo.php?fbid=997699724014529&set=a.101802853604225&type=3&theater
Oh yeah, she confirmed the teeth are separate pieces that were made somewhere else. There are also pegs for spines to fit in to Goji's back, maybe they were made the same way as the teeth.
Thanks Roger, for pulling together all that extra information. I sort of was guessing that about the teeth and extra spines, but it really is nice to have confirmation. I admit I am a little sorry that this sort of 'escaped' from M1 through the loss of the business, and it makes me wonder what else is out there. But I don't (and wouldn't) take this at all [FWIW] to mean that they begrudge Dave or anyone from rescuing these pieces. Sad that it happened in other words, but the mold will continue to be appreciated, and at least ended somewhere they know now. I doubt that it would have necessarily been 'revived' as this was a partial piece for a very specific special release in any case. PS - +333 bonus points to Roger for having all the inside track
Postscript: Dave offered to send the mold back to M1GO but Michi said it's ok. I told them if they ever want to produce these busts again, they know where to find the mold. ;p
Dang! That's a pretty awesome piece for the collection! Congrats! Looks like a great display piece that would appeal to kaiju collectors and regular schmucks equally.