I would not steer clear of the 606 due to fuel leaking prob's. After 200k I replaced all hoses, DV Orings & washers, and shut off valve Oring. Holy Crap, This engine ran like new(actually 50K when I purchased).
The only head problem I know of is if you break off a GP. I am not a great mech, certainly within this arena, but I have done these items in several hours for $300. Spread over the miles, I can take that, and I am looking for another instead of a replacement 603.
Wiring harness, trans wiring harness, spring perches all things I have not encountered on my '99.

Good Luck,

__________________
Gary
Experience is something you get, Just after you needed it....
'99 E300 295K, '83 300D 220K, '75 240D 185K sold
'80 MCI Bus Conv DD 6V92TA, w/4 cyl. Kubota diesel GenSet 12.5KW