The SL150 and SL120 are very rare in the US. We did have a lot of the SP25 and SP15 motor assemblies sold for broadcast DJ use
maybe that the SP-15/25 are much more common in the US and you can get them for a low price. Though most of them that show up on ebay look really scruffy & abused. Here in Europe they are much rarer and really expensive.
and they both use the same motor assembly as the SL1200 Mk II.
This is only partly true: the SP-25 does use the same motor assy, but the SP-15 does not. Different electronics, different motor, different specs.
The stock arm is very good when used with the KAB damper and retains the on the fly height adjustment for setting VTA. The molded, heavy base of the MKII is very good and I prefer it to the Technics base used on the SP15 and SP25. If you have not used the MKII arm with the dampener I would withhold your judgment.
I know the stock arm only without damping, and I didn't say it was no good - i said it's reasonable. Fact is, it works much better with a high compliance HiFi cart than with a hard DJ-cart due to it relatively low effective mass. Guess with the damping it improves on DJ-carts too.
The original question was more about the motor and yes the 1200 MKII does have the same -78 DB noise spec as the SP10 although the mass of the platter is smaller as is the motor when compared to the SP10 series.
It's not only the size. it's the speed accuracy and the torque that makes the SP-10 Mk2 by far superior to the SL-1200 Mk2. That said, I rate the SL-1200 Mk2 as one of the best decks ever made, especially regarding it's price.
All of these will plainly reveal the rumble of the cutting lathe the record was made on.
Well, hm, not on the records we cut, because our lathes are driven: YES - by Technics motors. The legendary SP-02 disk cutting lathe drive unit!
Compared to that the SP-10 Mk2 looks like a toy, specs are incredible. No wonder, the platter it has to drive weighs approx. 40 kg.