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All a bit of a learning curve but that's half the fun.
My prime source of information for the W165 is from the British Intelligence report No 1755, published in 1948. The report provided three cross section drawing of the W165 engine which you can see in Reply #11. One of the drawings had one or two of the major dimensions, which enabled me to accurately scale the whole model. I have made everything as close as possible, both inside and out, to the original, except for the cylinder blocks.8>< snip ><8I have been able to see and touch, one of the two surviving W165 cars at the Goodwood Festival of Speed and also at their home base in Stuttgart, Germany. Mercedes are very concerned about (pirate!!)replica engines and machines being built, therefore will not release any drawings and restrict access to details of the engines.