Configurations show a XM will fit a 30 hp Mercury. Could I use an XL ?

Opting for a larger size should be fine. Please use dimensions to confirm your setup is compatible with the larger size and other objects will not interfere with the swing such as ladders, power poles, decks, etc,. Installing a smaller size than is recommended can cause damage to your boat, the product, injury to you or others or even worse. If you have additional questions or require further assistance, please email us at info@turboswing.com Thank you for your interest in our products!