The Portfolio Template was designed to work for the X Portfolio post type. It's still technically possible to make it work for the Page post type but a lot of modifications to the template file would be needed. This and custom development generally is not covered in our product support.
I could point you to the right direction if you have WordPress development or WordPress theme customization knowledge though. First, you need to be familiar with X Theme Customization. We have a guide at https://theme.co/apex/forum/t/customizations-best-practices/205.
The file you'd need to modify is _portfolio.php which is located at x\framework\views\global. Following the customization guide, you already have an idea of what to do next.
The non-coding solution to this would be to use one of the bundled grid plugins as they allow the selection of post types and creation of custom grid skins so it's possible to closely replicate the X Portfolio built-in grid. Please see the items below:
Hope that helps and thank you for understanding.