One option would be to save your custom fields as postmeta. Normally metaboxes appear in the sidebar instead of within the post itself in the Editor, so that’s one difference you’ll face.
Once your data is saved, you will also need to create a template to display that data. Themes don’t search for and display postmeta by default, so you’ll want to first create a child theme by setting up a folder with a style.css file containing a few comments that tell WP your child theme’s name and what its parent theme is. Then, you can copy the parent theme’s single post file – likely single.php but could be various others depending on how your theme is coded – into your child theme. Finally, wherever in that file you want your custom data to appear, such as between the_title() and the_content(), you can get the postmeta and output each field wrapped in whatever HTML you want.