When I originally made Vickie, I wanted her on the (then only promised) 50 cm Obitsu body. When that finally came out I tried Vickie's original head (which is on the heavily modded 50cm BBB body now) a DZ Mo MSD head, on the 50 cm Obitsu body. Sadly the neck is WAY too big for that, and after considering K2s many suggestions for modding, decided that I didn't want to alter the Obitsu.
I just tried my Mei head on the Obitsu; it looks even worse than the Mo, VERY pinheaded. If you are married to the Mei sculpt, this is not going to work.
Now having said that, I think there are a number of small SD sized resin heads that probably WOULD work on the 50 cm Obitsu. Young Vickie is a discontinued SD (I think) DZ head. Yu? It's A GOOD bit smaller than the current DZ SD heads, about halfway between the SD and MSD size. As you can see here in the side by side of Young Vickie (left) and SWC Vickie (right).
Young Vickie: SMALL SD head on Obitsu 50 cm
SWC Vickie: MSD Mo head on BBB 50 cm
Now...looking at the various dolls I have, the Impl Heloise head is about the same size as this discontinued DZ head. That's a head circumference of 21 cm. Looking at the BBB stuff Emory has, he has an elf-eared BBB Yun with a head of 20 cm. I think that this head would fit very well on the Obitsu 50 cm body, and not look like bobbleheaded. You'll have to go NS rather than whiteskinned but if you are not married to WS, this combo looks like it will work.
I think we may have a winner.