With the possible exception of a bone-stock Babbit rod 216 or 235, 1,000 miles or so on the break-in oil shouldn't be a problem. A splasher engine will generate a bit more contamination as the bearings wear in to the crankshaft, so I'd recommend 500-750 miles on one of them. Modern parts are so much better machined and fitted than the ones we used 50 years ago that "break-in" is just about a thing of the past.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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