Well, Pel, define "
older Rumble 112".
Do you mean the now discontinued
Rumble V3 112 with the grille that matches the Rumble 500 combo? It can handle the 250 watts continuous that the R500c can dish out, plus it's the same width & depth as the R500c so it'll also look good doing it under the combo!
Or do you mean the even older
Rumble V2 112 with the black metal grille and the Neodymium speaker? IIRC it can also handle the 250 watts continuous that the R500c can output, but it's dimensions are different, a bit smaller, I believe, so it may have to sit on top of the combo. And that smaller size might not give the same rich sound as the V3 112, I dunno.
But, by all means try whichever one you can find first and let us know how it goes!
.