You will need to check the chassis number stamped into the right front frame rail underneath the throttle bodty to see if it matches the number plate that is screwed onto the firewall.
And yes, you are right, the code would be 10 for a stick shift, 12 for an automatic.
Unless the car is selling for a "What you see it what you get" price, steer clear, something smells fishy here.
The modifications needed to switch a car from automatic to stick shift would be extensive and it would be unlikely someone would have done this as part of a motor swap or other mechanical repair. I won't speculate further but the possibilities here, whether through innocence, ignorance or fradulent intent, are limitless and provably burried deep in the car's 43 year history.
Al
66 230sl
113-042-10-014715
904/396 blue, Ivory Tex
condition: not-as-rusty-as-before-bucket
