Where to buy remanufactured 230/250 L6

[chadvice]

Hello folks!

Newbie and first time poster here. I searched the forum threads first for an answer before posting here. I acquired a beautiful 1965 C10 about six months ago, and I've been working steadily to bring her back to life. I was told she sat in a Georgia farm field for quite some time. She has some bad knocks and has been hemorrhaging oil, and while I have been nursing that problem, I'm ready to pull the trigger on a new engine that my mechanic friend will be helping me install.

The current engine is likely a 230 L6 (if original), and I understand it and the 250 have the same geometry so either should be fine. I want to stick with the same engine for an easier install. I've been price shopping the parts stores (O'Reilly, Advance, AutoZone), and it seems they only carry part numbers DC74 and DC76, which apparently correspond with the later 250. It's not entirely clear what the difference is between DC74 and DC76. Another online vendor, remanufactured.com, mentions a part "DC30" that corresponds with the original 230, but it seems like it would be easier to just deal with a major chain like O'Reillys.

Any collective wisdom or experience on where to pick up my replacement 250?

Thanks in advance,
Chad