What do you mean by custom pages? Are you referring to landing pages outside of Marketo?
You can modify the LP Report to display any group of pages in the system. Go to Setup > and pull in the archived or unarchived icons and select Marketing Activities pages (in Programs) or Design Studio pages. Or any combination thereof.
Sorry - I meant "Landing Pages"
I notice some of those pages have data conversions; however, others dont.
I imagine I'd have to add code to define what a conversion is?
Notice The landing page has a form on it that I added using the embed code rather than click and drag - due to the design of the form.
So are you using a native Marketo LP or are you embedding the Form on your main website?
LP form fill out data doesn't seem to show up when you embed. I believe there is another thread on that issue and what you can do.
If you are using GA, you can setup goals and watch conversions there instead.