Malc,
As far as I can tell from Engelen, the manual and automatic engine numbers ran sequentially, but in two different series, and the engine numbers don't seem to relate to the chassis numbers, at least not in the 230 SLs. For example, the car being discussed here as the possible first 230 SL seems to have engine number 10 000001 (#1 manual transmission series production engine), but it doesn't have the series production chassis number (113 042 etc.). In Engelen's list of changes, the first 230 SL he lists is chassis number 3, so presumably there were chassis numbers 1 and 2, but who knows? Maybe this car with engine number 10 000001 is chassis number 1, but with a non-series chassis number? Or is there a different series chassis number 1, with an engine number that is something other than 10 000001? These are the questions that used to keep me awake at night, until I discovered Bombay Sapphire gin...
At any rate, later on in the series, the engine numbers don't add up and it appears that cars with the same transmission type built sequentially would not necessarily get sequentially numbered engines. The factory made a lot of running changes to the early engines, so probably a lot were used as test engines. For example, changes were made to the engines at two sequential chassis numbers 9094 and 9095, but (apparently) with engine numbers 1763 (auto) and 7773 (manual). Note that 1763 and 7773 add up to 9536, so it looks like there were 440 or 441 extra engines built. Which means James' car might be the 45th automatic car, or it could be some other number and the missing engines were test engines. Or, or, or... is it too early for a G&T?
So I'm not sure (cheers! siiiiip) there's a lot we can infer from engine numbers (sip) except as they relate to what is printed on the data cards. (sip) But it's fun to wonder.
George Davis
'69 280 SL Euro manual