First start up/first hour, you wanna use a an oil with a high zinc content.

Why? Because the zinc is an additive that bonds to the microscopic metal filings and draws them away from the friction surfaces. So on first start up, the fresh rings are gonna grind up against your pretty cross hatching, and wear the most they ever will. You want this zinc to pull this worn off metal away, and get it down into the sump, and caught in the oil filter.

As for the mineral or synthetic, HSV use Mobil 1 straight from the factory, which is a group 4 full synthetic oil. So use that to determine.

If you rebuild a motor to stock specs, and run a stock ecu etc, pretty much start it up, let it come up to temp, then go for a 20 minute smash, making sure you rev it out a few times.

Then go home, and change the oil and filter straight away.