I'm confused on what you are asking. You started out by saying the fields are in Dynamics and syncing down to Marketo but you can't use them as score fields... For this, the only thing you have to do is make Marketo see them as score fields which is what changing the type in Marketo will do. Dynamics should still be seeing them as the integer that you set them up as to begin with.
Are the fields in Dynamics and syncing down to Marketo? If not, you have to start there.