72" long and 1 1/16" wide at the handle is adequate for a 50lb bow given a decent stave. War bows need not be massively wider unless the wood is relatively weak and are made longer for durability, though sometimes at the cost of losing some cast if overlong.
Someone who sells bows is wise to overbuild in length for the same reason that a very heavy bow migth be longer. The work is spread over more wood and so the bow is less prone to taking on follow or breaking, all else being equal.
I have a bow that was 90lb at 28", tillered to 32" and it is 1 3/16" wide and 75" nock to nock. It was reduced in weight for field shooting by slightly reducing it's depth in cross section.
Another 56lb clout bow is 73" long and 1 1/16" wide and shoots a 500 grain arrow at 174fps with a flowing loose, 165fps with a slight hold at anchor.
In truth I think it un-necessary to go to 84" unless the wood is weak, or draw weight very high and durability guaranteed over cast.
Rod.
(Some equatorial hardwood longbows go longer, as much as 95")