Q: Will this Curtis oil drain valve (part # 05-03539) fit a Rotax 912ULS?
Yes, this will work for the Rotax 912ULS.
Q: Will the curtis oil drain valve /part number 05-03539 fit a Rotax 914 UL
Yes, this will fit perfectly.
Q: Dimensions for 05-03539?
12mm (1.75") x 1.335 long.