Switches for Atlas O81 track?

Ross custom switches makes an 080 that should work. You can use Atlas to Gargraves mating pins to put the Ross to the Atlas. 

The atlas rail joiners fit ross rails.  You don’t need mating pins. 

Do you have layout software?  I use RR-Track and it takes some playing around but it is possible with trial and error to get Atlas pieces to fit.  I think that there is some threads on here regarding other types of layout software and Atlas itself has a form of layout software but it is for Atlas track only.  If you can elaborate some more on what you currently have and where you want to go I could attempt to replicate and send you my results.

I just saw your diagram.  You will need an Atlas Numbered Switch and either a small O-72 curve or O-81 curve and some fitter pieces.  I am not sure that this totally answers your question but in this diagram all full curves are O-81 the switch I inserted is #5 with a O-72 11.25.  I also used a couple of 10" straights and quantity 2 1.25" straights just to again close the circle.  Does this help?

To insert a #5 in an O81 curve requires that there be roughly 12 inches of straights at both exits.

The RED track is O81 curves with 1.25" + 5.5" + 5.5" lead in and a 10" + 1.25 exit straights.  The BLUE track is the #5 and 3 x O81 curves plus a O81 cut in half (11.25°).

Jan