Unversioned content part records should derive from the ContentPartRecord class, versioned ones from ContentPartVersionRecord. The latter means that if the content part's data will be saved in the form of a new version (new database row) when the corresponding content item is published. A
ContentPartRecord can be migrated to
ContentPartVersionRecord as described here.
This page and many others here are part of the open-source, portable package of Orchard 1.x goodies: the Orchard Dojo Library for Orchard 1.x. The Library is freely accessible by anyone; just go to its repository to download its full content (you can even download the textual content of the Library as a big concatenated document in HTML), file issues or fork it! You can even edit it online on Bitbucket, just click on the Edit link in the upper right corner!
Note that the Library also has an Orchard Core version, check it out here!