If I had a site where I wanted to do this I'd convert the layout to a wordpress theme, and then import the pages -- playing with the URL format so that they'd correspond.
Creating a basic theme from existing HTML is pretty easy - see this tutorial for instruction:
You can leave out stuff you're not planning to support - for instance, you might not need the comments, gravatar, sidebars or posts if all you need is full-width pages.
If you can't replicate your URL structure perfectly with the normal WP custom permalinks options, consider redirecting with a plugin, like this one:
(I found this in the plugin directory, and haven't tried it or reviewed it closely. Evaluate carefully before using. ) A better option, if you can, would be to 301 redirect the old URLs to the corresponding compatible URL. You can use your .htaccess file, or a WP redirection plugin.