This pack is towards the end of a long line of adaptations for blanket carry. War is a great innovator. It should not be too hard to shave 16 years off it's design, getting closer to the American War period.
Warner Knapsack, so it will work fine.
The new interior will stick closely to drawing in the 71st Regiment's order book. The Inverness pack has a top pouch which will go away, but that makes the two side pockets bigger. Next time the inside.