First, if you want to know about Sunn cabs you need to use the best resource for all things Sunn; The Sunn Discussion Page
The Sunn Shack is very cool, and chock full of interesting and informative info but it hasn’t been updated in many years. The Sunn discussion page is slow moving but current. Lots of helpful posters there that have actual experience
with building Sunn clone cabs; unlike the "no real world experience" posters that will no doubt soon be hammering this thread, regurgitating "stickies" info as their own “learned” concepts; stickies that in and of themselves are often neophyte basic and not very real world cognizant, posted by wanna be speaker gurus in the first place.
While this often makes for amusing reading, this certainly isn't the best place if you really need good info.
Of course there are many excellent, knowledgeable and helpful TB posters who DO have a clue, and post useful info; however the truly sad thing about it is that it's often too difficult to wade through the “me too” pabulum posted by the "jump on every speaker thread and pretend like I know something" types to find solid and experienced info.
I wish there was a “clueless wanna be” filter available
Anyway, I digress… I think you are probably better off sticking with the 2X15 idea if you are trying for a Sunn clone. The 2X10/115 idea is feasible, but you might as well just start from scratch.
Might sound good, might not, but in any case would require a total reworking of the Sunn 2X15 concept anyway so what would be the point? I think the 36” high cab you refer to was the prototype garage cab, the production 200S was indeed 40”x24”x15”.