flange
Hi Mark. Are you using the highest tab (one closest to the sink)? On stainless sinks I find the mounting plate is very difficult to get started on the highest tab in the flange. Using the next lower tab will cause the the condition where you have the flange too loose, just as you described. I struggle with this each time I mount my KA or Viking disposals.
Two ways to approach this. If possible, have a friend push down, with great force, on the flange from the top of the sink. If you can compress the rubber rings enough you can get the mounting ring to just barely catch on the uppermost tab. It takes effort, but it will happen.
Secondly, do as Matt suggests and use plumber's putty as a replacement for the upper rubber gasket. I prefer the rubber ring myself, but you if can get the putty to compress enough the mount plate may slip more easily.
I always get the mounting plate to eventually catch the top tab, with some sweat and exertion, even if it just barely catches. Often, it is so tight, I cannot fully turn the mounting plate to the point where it is supposed to be. However, that great tightness will compress both rubber seals, and you will never have a leak.
I fight with this every time I install my KA so I understand your frustration. Once you get the mounting plate between the tab and underside of the sink, as previously mentioned, if you can't rotate by hand to is proper position, take a slotted screw driver and hammer and tap it so it will rotate a bit more. I often cannot get it fully rotated to the proper position, but get it as close as possible. When it's compressed that tight believe me, it will never rotate and fall down over time. I almost never get it fully rotated on a stainless sink, but have never had one come loose or leak.
Yes, just as Matt stated, often I have substituted discharge tailpipes. Try your Anaheim/GE tailpipe. If that doesn't work go to Lowes's and get an ISE tailpipe, or a generic flanged sink tailpipe.
The third option is to take a waterproof glue or epoxy such as JB Weld and use a toothpick and run it on the inside the indentation/groove of the rubber gasket, for the whole circumference. Put the lip of the tailpie into the indentation and wipe off any excess that squeezes out. Make sure none gets on the external surface of the rubber gasket as it has to stay pliable.
Wishing you well on your installation!