I'm assuming you are talking about your 450SEL in your sig...

Looking on EverythingBenz - Mercedes-Benz Forum and Web Search Using Google it seems as though your M117.986 was only "factory" mated to an automatic transmission (722.001 or 722.004)

I'm not sure if there was ever a factory manual transmission option for this engine. You could go through the list shown here to check =>

Mercedes-Benz M117 engine - Wikipedia, the free encyclopedia

If there was never a Mercedes manual transmission fitted to this engine then you've got a bit of an uphill struggle working out how your custom flywheel needs to be designed...

...well I guess you need to seek professional advice on that one.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!