I may have figured it out and the solution is kinda dumb.
So my print file is 5 inches wide in illustrator (I’m using inches because the job requires that size)
I change my illustrator document setup to points. It is now 360 points wide.
I merge my illustrator file into c4d and in the illustrator scale dialogue I do this math 5/360 =.0138
so the scale is .0138 inches
Maybe I’m dumb and there’s an easier way which allows me to use inches in my print file. My 3d printed does use mm so I will have to convert again. I wish this was easier.