Have you tried this SEO package?

My current site https://www.redlinestands.com experiences better rankings for sport bike stand searches than any other site on the net. I attribute this highly to my urls that contain tons of great keywords so I'm a bit cautious about converting to a zen cart site and loosing those great urls. So, I've found the package linked below. I'm curious to know if anyone likes the package linked below or if there is something better?

Ian
http://www.zen-cart.com/index.php?main_page=product_contrib_info&cPath=40_47&products_id=231

Migrating from a html site to a php site will cause you to suffer at some level no matter what you do.
You can create the many permanent 301 redirects to mitigate the loss.

I would goggle for magicSEO and it is a for purchase module but does a respectable job

Whichever you want, I will recommend staying away from ultimate seo url. It does not have any official support, the author is long gone.