More specifically, he might be putting a new turbo on a wrecked engine.

OP, before taking this risk, I'd say you should do/get done everything possible to check out your engine. This probably means finding a good diagnostician, a good trick if you can do it.

As well as the conventional compression test, endoscopy, oil analysis, turning over by hand, and perhaps other stuff I havn't thought of there is a thing called a Relative Compression Test, (look it up) which measures and records current draw on the starter as it turns over the engine.

This has the advantages that

(a) You dont need special high pressure diesel gear (but you do need an expensive scope)

(b) Used with the cylinders decompressed (injectors/glow plugs out?) it might, with experience, give clues as to the state of your bearings.

You'd need to find someone to do it and interpret the results though.

Dont think a definite diagnosis is possible short of an engine strip, only indications.

(Another possible indication that I forgot would be measuring oil pressure.)

One of the possible indications doesn't require towing anywhere, just posting off an oil sample.

Ultimately though, whatever clues you collect, it comes down to whether you feel lucky or not. I hope you are.

In future (Assuming there is one, which seems reasonable) perhaps worth trying to find out what the highest viscosity permitted (not just whats recommended) for that engine would be (assuming they allow you any leeway at all) since a higher viscosity is likely to give mildly compromised bearings an extended lease of life.

Didn't think of that, though I should have. Perhaps I didn't because I've only ever had cars that would require you to cut the filter open to examine its contents, but maybe this one has a removable filter element. A relatively straightforward post-incident check.

TBH it sounds rather bad, though of course I havn't seen it.

One might consider getting the filter debris analysed (or just looked at by someone experienced) to try and asses where it came from.

Could be, most obviously, from turbo bearing breakup, or t could be that there is a failure elsewhere that has lead to the turbo bearing breakup. Either way, it suggests you have had circulating junk in your lubrication system, which wont all have been stopped by the oil filter and has likely done systemic damage.

I'd probably get an oil analysis done before finally calling it, but its not sounding such a good bet now.

Cylinder 3 comment is too vague to be interpretable.

No obvious (to me) connection between injectors and your lubrication system, so either you've got an independent fault, or the vibration reflects knackered bearings, (perhaps describable as "rod knock", though a mechanic should recognise that), or bore wear