Doug:
As you know, I have one of your UBH's and like it enough that another is on order along with your version of the e>C adapter. I also have a 3-cell McLux body I like (but not as much as yours).
The D3 bodies can be extended with A14's and A19s. This is necessary when I drive a P91 or MN16 with 2 @ LRB168B Lithium-Ions or when I drive my N62 with 4 @ CR$123's or my MN60, or MN61 with any workable combination of Li-Ions or CR123's.