First, don’t beat yourself up, your experience is not uncommon, and can happen to very smart and experienced people. There are 100s of posts on many automotive forums that describe very similar scenarios.
As anal as I think I am, and as smart on research as I think I do, I still get scammed and screwed.
On engine rebuilds, the machine work, bore, hone, crosshatching, and RA are critical for the right ring and piston selection. Based upon what this guy has been telling you, he’s clueless, BUT apparently not completely unscrupulous.
Typically, the rings should seat within a few hundred miles. Rotella 15-40 comes in conventional, synthetic blend, and full synthetic. I think 15-40 is not commonly recommended for this rebuild.
Keep track of your mileage and oil consumption. I’d pull the spark plugs and see what they look like. I’d do a compression check now. I would make darn sure what the valve lash spec is for the cam and recheck the lash again in a couple 1000 miles. Recheck and tighten your exhaust nuts - they should take a set in about a few hundred miles. Document everything you do, so if you have to go back on his “warranty” you have some proof.
So far it sounds like he has rebuilt it to “spec”.
Thank you for being so candid about your experience and taking the time to detail it here.
It is a great lesson learned, and highly educational to know about.
Please keep us posted.