If you do a complete cylinder head rebuild, you will be rewarded with:

An engine that uses 1 qt every 500 miles.

An engine that may bend rods due to new found power.

Really, having good valve sealing on worn rings will draw lots of oil into the combustion chamber. Not only will oil consumption increase, compression ratio does too.

Your friend that has worked on some diesel heads, is he a mechanic or someone that has done some at home repairs? If mechanic, is he heavy equipment or light truck?

Him not "skimping" and wanting to throw every part at the head could be considered not knowing what parts are worn but are reusable Vs what parts are too worn to continue. Another consideration is that heavy equipment engines need to run at full power for extended periods so they need better parts what would survive in a lightly loaded automotive app.

There is always a risk in patching up a worn engine and something will always be left undone. If you do all those "just one more things", you end up with a rebuilt engine.

So, if this engine was running and driving, would you have removed the head for a total rebuild? If not, pull the head, change the prechamber, look the head over for obviously burnt valves and reinstall. ( exhaust valves will always leak a slight bit on a worn motor )

The next step, if the car is worth while, have a spare engine waiting ready to go. A 606 swap is probably beyond your level due to mods needed, but a 3.0 603 is supposed to be a drop in, others can speak to the specifics.