I've used Brad Penn Penngrade1 30wt Break-In Oil with good results, switching to 10W30 after break-in.

And yes, as you know, there are lots of 10W30 break in oils available. A quick search at Summit brings up 10W30 break-in oils by Comp Cams, Royal Purple, Driven, Lunati and so on - but I've never tried them.

I have used Red Line Oil's Break-in additive in a more modern engine that I intended to run Red Line Oil products after break-in, and that worked well, also.

1947 2nd-Series GMC FC152 3/4-ton
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1953 Chevy Bel Air Sport Coupe Powerglide