It is my belief that the 11.8" ring gear still utilizes the same housing as the 11.5" axle. That's why a common upgrade for us non-Aisin folk is to purchase the Aisin aluminum fin housing and stick it on our non-Aisin rear differentials (just waiting for my dealer to receive it since it is a back-ordered part for Mopar). So yes, the SRW trucks still get the 11.8" ring gear, but the rear axle housing is the exactly the same as the 11.5" axles. Now the aluminum finned cover is a different story. That cover is only included on Duallies equipped with the Aisin transmission, regardless of rear gear ratio since all Aisins come with the 11.8" ring gear, just differing reductions (3.42, 3.73, 4.10). But it's only $90 to $130 to buy the finned aluminum cover and slap it on your truck the next time you're doing the maintenance on that rear diff (much cheaper than trading for that dually!).