Hello Rod, good to see that someone else is working with this format.
In case it's of interest, this is my version of what I call the "six-and-a-half-frame nuc" !
The difference from your own approach is that I use a slide-able divider which lives in the box permanently, so that correct frame spacing is maintained.
In 1x6 mode :
In 2x3 mode :
The covers are placed on top of the box, so that a beespace is maintained between frame top bars and covers :
And like yourself, I much prefer telescoping covers ...
The only downside to my approach is that the divider takes as long to trim to size as the rest of the box takes to make (!), as it really needs to be a precise fit. I've made 8 of these so far to test as initial prototypes, which are now fitted with low profile overhead feeders. So far, so good.
Best of luck
LJ