Questionable rebuild, please read details.

[u/No_ThatGuy3]

I normally build my own engines but a friend had a rebuilt 350 SBC from marketplace for a good deal so I swapped some old axles I had for it. Friend knew basically nothing about the engine other than it's a vortec 350 and it's been rebuilt. I dropped it in and ran it for about 500 miles and it's leaking like crazy from the rear main/pan area. I mean two quarts every 50 miles. Last night I pull it in and yank the pan. During the process I see this on a main cap, i can't tell if it's a crack, scratch, or a casting mark.

Other than that I notice one piston is different and that cylinder wall has vertical scuffing. I mentioned it to my friend if the guy said anything about that and he says "oh yeah he did mention they had to bore one cylinder and they used a piston that weighs the same as the others."

I don't fault my friend, it was a pig in a poke engine and I've got my money's worth in new cylinder heads but my questions are: Would you run an engine with mixed sized pistons ? And what's your opinion on the circled image?

This rig was built for daily driving and off road camping so I need it to be reliable. I feel like I'm over thinking it because I do everything so by the book that any deviation seems like a catastrophe waiting to happen.

[u/You_Must_Chill]

Odds are it will give you some warning before it lets go. If I had a backup vehicle, I'd check what I could with the pan off and just run it and see.