IMO, a D30/35 combo is very safe with 33" tires. You can still break it, but it's safe. A 35-37" tire can be wheeled safely but it takes someone with restraint to keep from breaking them. I wheeled mine pretty hard with 35" Krawlers before I broke them............... but I eventually broke them. The way I see 2fst4u driving, they won't last long.
I don't see a big plus to tacking the caps in place. Sure, they eliminate the snap ring from coming loose but in most of my axle joint breaks, I broke the pin off the spider or twisted out an ear. Snap rings were still in place.