Migrating from Joomla to WP

Hi

I’m about to migrate a Joomla site into WordPress (or rather, build it from scratch). The user has asked if their Google ranking could suffer… it’s the some domain-name (and hosting package) I assume that if I make sure the filenames match the old ones I should be okay? I notice that (unlike WP) this Joomla version has a convention of no trailing-slash URLs.

Is there anything else I need to consider? Any help would be gratefully received.

Thanks in advance

Jez