Mariposa Plum AIr Layer

DavidL starts with ...
I have heard that Mariposa makes a reasonable rootstock (not sure if that's true!). Anyway, I air layered a few things for the fun of it over summer, and the Mariposa has taken (also got some other things I'd had no luck at with cuttings, so it's been worthwhile). Does anyone know How it is it likely to go on its own roots? (The parent tree fruits OK despite a terrible location under big gums, next to a Santa Rosa). If I do another Mariposa air layer, would a simple wedge graft of Santa Rosa on an eventual side branch - maybe next year - be sensible, to get the same combo at another location on the one tree?