Well, that is can't go wrong advice.

Do you know why the crank broke? I've never heard of a mb crank breaking before.

To do it correctly you will have to remove the cam chain as a minimum. At that point it makes sense to replace all the cam chain guides. Removing the crank without removing the head will be very tricky to say the least but it might be possible. I'd think going through the engine and replacing whatever is deficient would be a good idea.

Did you try to find a known good used engine?

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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.