The frog's ARE completely different. It's odd that the Shelton #9 is the only Bailey pattern plane that Shelton ever made and it was a post WW2 addition. I have stopped buying planes, I don't have room for a wall of plane in my tiny workshop. However, that said, I'm keeping my Miller Falls, I just like the way it looks.
Shelton plane company was around since the early nineteen hundreds if I recall correctly. Some of their earlier planes had a unique adjustment mechanism, some people collect the early ones but they are not regarded as good users. A search on E-bay will likely turn one up. I may be incorrect but my understanding they where bought out by Stanley at some point and may be reason for Bailey design being used. I suspect they where a lower cost plane to market to retailers so as not to ruffle the feathers Stanley's regular retailers. I have three Shelton number nine planes (they are cheap and kept popping up and make a good fore plane or for rough conditions), one doesn't have a frog adjusting screw, but he other two do. Seems like most you will see have the ugly ass totes like yours and one of mine. One of mine has a tote that resembles a very nice Stanley and the other is some where in between. The thing is if they are tuned they can actually work pretty well although all I have seen have a large mouth, but can be adjusted with frog. As far as Miller-Falls they made many different versions of the four size smoother plane some with solid lever cap. The ones with two piece lever caps are considered much better planes. I have a number nine that planes as well as any Stanley but the back lash for blade adjustment is so horrendous that it doesn't see much action. Hope this answers some of your questions.
