If you go to the Winnebago product site
Winnebago Ind Product ResourceClick on the Resources tab, go to Motorized Parts List, you will get an option to type in your Winnebago serial number. That will pull up a complete parts list for your specific unit. Using their parts catalog, it will show you the exact item that came in your unit along with the description and specs. If it shows no actual range originally installed, it will list the cabinet part number and that would tell you the opening size of an oven that would fit the cabinet.
1994 Itasca SunDancer 21RB - Chevy G-30 chassis.