oil question on fairly new engine build

I would run it for about 500 miles and change over to mobil 1 synthetic.
My dad bought a new 360 78 powerwagon after the first oil change, he went to Mobil 1 back in 1978.
At 213,000 miles clutch finally wore out.
Dad said to freshen up the motor while it was out.
I pulled the motor, and there was no wear on the bearings.
Re-gasked it still going strong with 244,000 on it right now.
There is only about $3.00 difference per quart on dino and synthetic.