K301 versus K301AQS, what are the differencers?
 

Between lets say a K301 as installed in a narrow frame i.e. CC127/125
versus a K301AQS from a 1210.

I have a line on a "good running" AQS along with the tractor for $150.
If the engine can be use as a transplant into a 127, I might buy it.

If you strip the two blocks, they will interchange. Tins are different, flywheels, rear bearing/closure plate, carb, throttle linkage, cylinder head, exhaust elbow, dipstick tube and governor arm..... other than that.. They are the same. LOL. (I don't think I left anything out.) Do you need a complete motor? Like, do you have an engine? Or is it missing entirely? (For the narrow frame.)

I have one running 127.
One 127 with thrown rod bearing windowed block.
One 126 with no carb, gen, muffler in unknown internal condition.
I was only looking at the 1210 as a donor.
Do not really "need" it.