Just copy the stuff inside your site's "blocks" directory to the new site's "blocks" directory (make sure you're in your site's top-level blocks directory, *NOT* in concrete/blocks).

After you've copied the block directories over, you'll need to install each one via Dashboard -> Add Functionality. Note that you will also want Designer Content installed (even though you don't need to use it to re-create these blocks or anything) otherwise the editing interfaces on some of them will be wonky.

AMAZING! Do you know if it's possible to change the directory name? I would like to change "bio_block" to "leadership_bio_block" for example. Would this break it?

(I'm talking about changing the name PRIOR to uploading it to the /blocks directory and adding it through the Functionality panel)

You can change the names (as long as it's before you install them via the Dashboard), but in addition to changing the name of the folder you also need to edit the controller.php file of the block and change the class name as appropriate. For example, if the folder was called "bio_block", the class name would have been BioBlockBlockController, but now if it's leadership_bio_block, the class name would be LeadershipBioBlockBlockController (basically, the TitleCase version of the folder name followed by "BlockController" -- kind of weird in your specific situation because you also have the word "block" in the block name, so you wind up with "...BlockBlock..." but that's okay, just something to watch out for).

Hm, well I changed the directory and the class in controller.php but it still shows up as simply "Bios Block" in the Add Functionality panel. I haven't installed it yet. Is there something else I need to change? Perhaps $btName? I see $btTable also has the name in there as 'btDCBioBlock'...

Oh yeah, change the "Name' ($btName). Don't worry about the database table -- it's okay for it to stay what it was (if for some reason you do want to change the database table name, though, you will ALSO need to go into db.xml and change it there too)

Thanks again!!

You're welcome! Good luck with the rebuild.

My blocks aren't showing up in the add functionality section. They are being transferred as is from another site. Is there any reason for this?

This is a general Concrete5 thing, not specific to "Designer Content". For whatever reason, they've split up the installation of addons (aka "packages") from the installation of custom blocktypes (which are *sometimes* part of an addon/package, but other times -- like if you create your own with Designer Content -- are on their own).

Long story short: go to Dashboard > Stacks & Blocks > Block Types, and install it from there.

-Jordan