Wordpress - Importing old blog with regular posts into new custom post types

As an alternative, when you use the Wordpress Export tool, you can open the XML file that is exported in any text editor (I used Notepad++).

I did a simple find a replace on this line:

<wp:post_type>post</wp:post_type>

and replaced with:

<wp:post_type>blog</wp:post_type>

This took all my old "posts" and made them into my new custom content type "blog".

Then I just imported into the new site, that already had a custom post type called "blog" and it worked flawlessly.

Try importing and then using a plugin (Post Type Switcher) to change the type. There are a few other plugins out there for this, I seem to remember one which would convert multiple posts, but I couldn't find it just now.