If we ignore the fact that Motown bass lines were recorded using custom made valve preamps, you can get that tone out of many cabs these days. The main ingredient will be a Precision bass with flatwound strings and maybe a lump of foam. I believe Tommy Cogbill recorded many of the classic Soul bass lines by mixing DI with a Fender guitar amp.
I practice with a Jamerson tone at home, through my P bass, flats, foam, Thunderfunk and 2 Barefaced One10's. Pure Motown and not a 15 in sight.
If you really can't get your head around the possibility that a 12" cab can be better than a 15" cab, I'd second the Barefaced G2 Compact suggestion. You probably don't want your 210 in the mix for this idea.