I think your best bet is to drain all the oil out you can and fill with the quantity of oil specified. Looks like 4 liters at 7 degrees. If you're changing the filter add a liter. more or less. Not to worry about the cooler unless it is equipped with a drain. After all that look and see what you have on the dipstick.

Trying to measure the dipstick without having proper measurements on it is guesswork IMHO.

As for blowby, there is an oil separator on 240s when installed in a car so if its functional you should not need the pop bottle.

Can you post up pictures of it for us to look at?

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.