Notice also how the early spits (without the smoke hoods) were meant to be used without a lid. Looks like they just clamped to the bowl.
Webers main competition at the time was Big Boy , they both attended all the trade shows and did cooking demos , sometimes side by side .i think Weber was getting " showed up " at these events by the Big Boys Roti set up and so they had to get something in the works to compete. The hood looks like a Big Boy brazier set up and likely spawned the roti ring . Once Weber started having the lids drawn instead of spun they added more height to accommodate large cuts .
In this early brochure they don't offer a roti , claiming there's no need for it .
In this 55-56 photo they have the clamp on version , but the lid didn't have clearance to be covered so I'm thinking this was among one of the reasons for the re-design
* this is only my opinion
" Esto Perpertua "