Hallo,
I own a 1984 hymper camper with 309D chassis and 617 type engine,has anybody links/info on converting to a turbo version by engine replacement or other means???
\ I need more torque and slihghtly more topspeed

The non-turbo engine is not designed for a turbo and can't handle the added stress, especially in a van where its working hard all the time. Despite the 617 engines looking similar on the outside, inside they are completely different.

A turbo engine could be swapped in but it would be a tight fit. Especially on the right side where the turbo lives, you might have to alter the body for it to have room.

Adding a turbo won't increase your top speed if its limited by gearing.