Rebuild my donor engine or not? And strupped glow plug thread

[Souster]

Hi all

Need your opinions please on the engine condition please....
Finally got my hands on a 300tdi, it's actually still in a discovery 1 MOT fail. It's done 150k miles. 

Now the engine sounds sweet as a nut, starts on the button from cold with no blue smoke on startup, Just a small black puff. When cold there is zeropuffing/breathing/steam out the filler cap or dipstick, a very slight bit of steam when warm out the filler cap. Only a fraction really that can be seen with a torch in the dark. Is that a sign of wear? 

The engine pulls like a train, and thedifference is black and white compared to the engine it's replacing in my defender. 

I managed to get some compressionreadings when warm. 
Cylinder 1: 380
Cylinder 2: 380
Cylinder 3: 390
Do these sound good to you guys? 

Now unfortunately, I stripped the glow plug hole on cylinder 4. I managed to getthe glow plug back in and not losing any compression on tick over. What are my options here? 

So my question is, it seems to good to strip down and rebuild, when it's running so well. What would you guys do? 
Obviously the engine has got to come out. Would you rebuild it? Or Just put acambelt, clutch and crank seal? Orsomething else? 

It also doesn't leak. 

Thanks in advance guys