Alright, an update.
This past weekend, I had a little free time, so I decided to do a quick test-run on the Guardians customs.
Pardon the crummy cell phone pics, but this is just a rough run-through, anyway.
First, after doing a couple of hot water head-pops, I discovered...
Despite the heads being essentially the same size on the Movie Masters scale and the (supposedly) 3 3/4" scale, the neck posts to those heads doesn't come close to matching.
This isn't a huge deal, just a little extra work for me and my Dremel to bring the post down to size on the Movie Master. (The other options would be to try to enlarge the hole of the 3 3/4" heads, but there is not a lot of room for error there, or to "transplant" the post from the smaller figure, but that would make the attachment weaker.)
Side note: Funny thing about these heads - the small ones, in my opinion, are niceer than the Movie Master heads. I prefer the shade of blue on the Movie Masters, but the sculpt, paint details, and translucence of the 3 3/4" heads is better. The Movie Masters are virtually one solid paint color and the back of the head is almost as opaque as the face. As a result, I have now invested in a couple of those individually packaged 3 3/4" Kronas, so my Guardians will match.
Anyway, here is the look at the results of the first pass, paint-wise. It needs to be cleaned up and is far from perfect, but will give the general idea of what I'm going for.
Pre-paint:
Post-paint:
My initial reactions: I'm thrilled. The white breaks up the red, and I think it looks much better. When all is said and done, I'm planning to have at least eight Guardians for my personal collection - the seven head transplants from the 3 3/4" figures, and one with the original Krona head. (Admittedly, I waiver to and fro when it comes to beheading Herupa, Ganthet, and Scar, as I have seen the prices these figures are going for on eBay, but that was always my intention, and I have enough plastic crap laying around that is supposedly "valuable" - I want the larger figure set more than I want the money.)