Hi!
Actually, adjusting the permalink structure like this should work, yes. However, s9y might use a different method to rewrite entry titles to HTML. WP might rewrite a topic like "Hey, Folk's!" to "/2007/07/07/Hey-Folks", while s9y might rewrite it to "/2007/07/07/Hey-Folk-s!".
If you have that, you might need to either change the original title so that the automatic URL of s9y looks like the former WP URL (by removing/replacing characters), or you would need to insert a custom rewrite rule for every entry where the permalink differs.
BTW, you can use the permalink "%year%/%month%/%day%/%title%" for s9y. I usually don't suggest to not use a "/archivs" prefix, but in recent s9y versions this works more reliably and should work fine for you. PLUS, you also don't need the ".html" suffix anymore. Have a try if it works. If it doesn't, we'll find you a regex.
Regards,
Garvin