Of course, a B-15N had NOTHING to do with Motown. 
I'm not sure what you're getting at here, but I did not say anything close to that.
I find the Altecs to be on the trashy end (tone-wise), but I'm not sure I've ever used the 342B specifically - at least not the power section. The current prices on them are insane too (I totally missed the boat on that, but at the time I was grabbing up Ampexes which I like better) though Ampexes can be way up there too, price-wise, it's mostly the 350/351 and 601 that are expensive; moreso than the PR10/354 (which were seen as dogs due to the PR10 transport), and the 'better' ones have only 1 channel vs 2 and some of them require an external power supply so cost more to get working stand alone as well after you buy them). The 354/PR10 are still bargains by comparison (the MX10 is likewise expensive though, especially if gone over/modified - not worth the price IMHO, but you can sometimes find them cheap in random places) these all sound rather different from the predecessors (350/351 and 601) which is what I am assuming you have some of, because they were the ones that were better known for their sound and more desirable/first cannabalized for stand alone use vs the others (the 350/351 certainly look cooler - and it's what they based the look/sound of the Ampex sim DAW plug in on). Anyway, it is rather well documented that Hitsville used MX10s - they had a prominant position just to the left of the console (bottom item in the rack, with other Ampex units in the rack around it):
Though they also had a single Altec (not the 432B, looks like a 1567A, so similar in that it's a powered mixer) in the back rack and I know that at some point (later than these pics I think) they had some Altec compressors in that same rear rack:
(click either for larger)
Anyway, I guess we're hearing different things. Tone is sso subjective. JJ himself didn't always sound the same on every record. Sometimes he was really mellow like this:
and other times, while still his mellow self under there, he's dirtier with a certain upper middishness - probably to cut through busier mixes easier, like here (really obvious before the drums kick in):
The second one definitely does not sound like Ampex to me; but who knows what was in the mixing chain - the whole song sounds like the upper mids were turned up on everything (or at least the entire rhythm section). The first one does however sound ampexy to me (Ampexes can get dirty, it just doesn't sound like the dirt on the Ain't That Peculiar bass track when they do).
Anyway, I'd say at least 80% of JJs tone was his bass setup (dead old dog flats) and his fingers.
