While it it true, there is no rod and tube level indicator, Kubota does include a level indicator of sorts. On the bucket itself is an L shaped piece of metal welded on that is in parallel with the bottom of your bucket. When you sight across this this metal strap and it appears to be level, well then the bottom of the bucket is also level. Yes I know it is Mickey Mouse, but it does work. Especially after you use it for a while, it kinda grows on you.

Of course you can fabricate the rod and tube type yourself if you wish. There are several threads on here of guys that have done such. Basically a tube attached to the stationary end of the curl cylinder pin or e clip. and a rod attached to the center of the pin of the moving end. My Kioti has a little bracket welded onto the tube end of the curl cylinder itself, and the rod is threaded/bolted to this little bracket. Unfortunately I don't have a photo of the lower attachment bracket, only the upper.
I have seen the L shaped brackets. I will not be the only one using the loader and need something Fool proof. Thanks for the photo, I think it will help me fab something.