based on what?
From where you drew those calculations?
Not calculations, just rough round-number estimates.
I'm thinking that they wouldn't occupy foundation as densely as comb. / ?? True?
He has some shallow drawn comb. (about 5 inches deep)
He has only foundation in the deep size (about 8 inches deep)
If he uses the shallow, its space now, (about an extra of 62% in comb area from his single deep box now) but the deep would give him more space (100% more than before), but not fully effectively until it is drawn.
And in this weather, in the North of England, my expectation is that even his full box of bees, being fed, would take at least a week to draw out the foundation.
Because of his brood-break, the number of bees in the colony will be reducing. So the overcrowding will be reducing anyway. Every day, fewer bees.
My suggestion is just that some extra comb, now, is probably a better bet than the hope of more, later.
Also, and on this I may be entirely wrong, but my expectation is that wax-making would be similarly hard (and life-shortening) as intensive foraging for the workers. Which leads me to suspect that, with this weakened colony, asking them to draw another full box of comb would increase the daily death rate, causing the population to crash to a lower level, before the numbers start increasing. And that means fewer bees to cover the new brood, making for a slower build-up when the recovery starts.
As I indicated YMMV - different people will come to different conclusions.
If you think they'd be better with the bigger box of foundation than the smaller box of comb, I'd be interested to learn from your reasoning.