M42 rebuild and probable turbo in future

[Diake]

Hi guys,
I own a pre-restyling 1986 316 E30, and I've bought everything I need to swap to M42.
With that in mind, since the engine has seen better days and I'm not sure about its the past history, I was thinking about rebuilding it (also because I like doing those kind of things on my own, still not excluding shops for detailed and precision jobs). I also planned to turbo it in future, but due to actual lack of money and time, it's a long term project, and I want to drive it in the while, even if it implies spending more to turbo it in a second time (I aim at 250-280 hp at the end, nothing crazy, but without E85 since it's not available in my country).
That said, what do you think are the upgrades worth doing and what should I just refresh/leave? I read a lot of threads and I've understood that the weak points are the timing chain and gears, the oil pump and oil pressure relief valve. Moreover I tought about upgrading radiator and fuel pump since I have to swap fuel tank. Which one do you suggest? Any other sugestion?
I was planning to do a build thread, but this will happen in a while, since I'm abroad for studies for some months.

Thank you all in advance and congrats for the awesome forum and knowledge

Luca