Cheapest usually is to find a wrecked car. Preferably a 91 and up 3.5 liter diesel with a failed lower end. Buy the car or #22 head off it. You really do not want another #14 head for money.

When the lower block on those 3.5 iiter cars goes bad they are usually either quite cheap to buy or consigned to the junk yard. Also that head may not show as a direct cross refferance at auto wreckers as you need some external parts with it to make it work on your engine. The 3.5 is just an overbored 3 liter 603 basically.

Mercedes did a sort of flip flop. The early 603s had almost bulletproof bottom ends and questionable heads. The much later 603s bored to 3.5 liters had really good reliable heads and unreliable lower blocks.

So if you take the old short block and install the newer head you have a really strong long lasting reliable engine. Mercedes is engineered like no other automobile remember.

I kind of have to agree with their 603 engine design types. I can almost see the design team saying. We will massively improve the defective head problem and change the know bulletproof short block. They reasonably could claim they built a solid diesel engine head and a solid lower block . It just never occurred to them to sell the combination as an assembled package apparently.