Without going into detail, this approach simply will not work. The main reason is the fundamental difference between DYNAMIC content and STATIC content, and the fact that PHP performs hundreds of FUNCTIONS over-and-above its role of cobbling together a web page.
If you pursue this route, you are not only wasting a LOT of time on a pointless quest, but you are putting the functionality of your client's site at severe risk - not only from a performance point of view but also:
Security and User Data safety
Session Tracking and Management
Bi-directional communication with payment gateways
Search Engine analysis and indexing of your site.
If I was your client, you would be immediately FIRED !
Do the job properly... what you will deliver will be a dismal failure, then your client will blame zencart.