Hey Matt Stone,
I know exactly what you are trying to do. You have to call support and tell them that you want to remap the default opportunity amount field in RCE to a custom field. Not everyone in support will understand what you are talking about. Devyn has done this for me out of Portland support center. It is possible. You might run into 1st line support folks that say its not. It is. The caveat to that is you have to force RCE to recognize the update so you have to make an update to all records in SFDC, like adding a period to a field in SFDC that syncs to marketo. I'll be at Summit so reach out if you need more help.