Mine is 51 1/16 x 23 1/16. I assume it is a more sensible number if you have a metric tape. Good luck! I have a 1975.
Hi Maggie: Thanks for the measurements. I had to add about 1/4 to 1/2 inch here and there for rockguard to fix the window. It turned out well and I have to look on this site for directions on how to show pics. Thank you for your help!-Mary Lynn