In addition the lifeboat count, Britannic had very large gantry-type davits installed to handle the extra boats, many of which were stacked. A shop on Shapeways (not mine) offers those. Link:
https://www.shapeways.com/product/3XZU57TZR/britannic-gantry-davits?optionId=42999233&li=marketplace
The A Deck deckhouse below Funnel #2 is a bit different. Britannic had a children's playroom added port-side which looks almost like a mirrored version of the starboard-side gymnasium.
The aft well deck is covered. A large deckhouse was added to the forward well deck to provide, among other things, a protected entrance to the bow streerage class areas.
I have saved a page from the old TRMA website with descriptions and drawings. PM your email address and I'll send you the page.
Hope this helps.
Steve Larsen