Create the layout "upside down". Use a font editor to create a custom version of your arabic font where each arabic

font character is rotated by 180°. When you enter these "upside down" characters in Finale, in Finale's usual

"left-to-right" manner, the character will run "right-to-left" when you turn the printed page upside down.

Hide the real time signature (12/8), and create a false time signature as an expression.

Use the Shape Designer to rotate the time signature 12/8 "upside down".

To do so, use an invisible line (= 0 thickness) with a "custom arrowhead" that consistes of the number.

When you draw the invisible line right-to-left, the arrowhead will be rotated by 180°.

You might want to use a horizontally flipped version of the Maestro font. When you use the "rotate text" trick I

mentioned above, on the horizontally flipped Maestro font, you will get clef symbols and flat accidentals that look

right.

I can't speak for Arabic, but I have notated Hebrew music normally, with each sung syllable in Hebrew being right to left on their respective note. I've never seen the notation reversed, and a Google search didn't, either.