Export the 30 frames per second and 60 frames per second as 24P.
What is the difference in the final quality with the two mixed?Any?
I've always heard there aren't any good ways to convert 30p to 24p -- that it never works.
Can't you merely have some clips play at 30 and some at 24?
I feel like we're making much ado over nothing. 30FPS dropped into a 24FPS timeline is just fine. Filmmakers might notice that something is off. Non-filmmakers won't know the difference. Go on with your bad self and mix those formats!