Here's a 1950 CJ3A with a WWII top and bows, but using a CJ2A windshield. It
can be done but you will have to get accurate measurements and drill the holes for the top bows in the exact right place at the correct angle or you'll never get the canvas to fit. The real problem will be attaching the canvas to the CJ3A windshield. The WWII top doesn't have the correct features to match up to the windshield. A WWII windshield has a series of individual buttons along the top of the windshield frame. There are matching holes in the top to hook over them. A CJ3A windshield has a horizontal slot across the top with a corresponding ridge in the canvas to slide into it. Completely different. Then there is the issue of windshield height. The CJ2A is approx 2" higher than a WWII windshield and a CJ3A is approx 2" higher than a CJ2A windshield. As you can see in the photo, the WWII canvas top runs in a perfectly straight line from rear bow to windshield. A WWII would drop down slightly from the center bow to windshield but on a CJ3A it would angle upward which, in my opinion, would look odd. And finally, the top edge of the WWII and CJ2A windshields are flat, straight across, but the CJ3A windshield is curved. I just don't think there is any way to make it look decent.
I wouldn't do it but that's just my $.02.

Larry