When egg size is not specified, you should assume large.
The differences in sizes between eggs is 1/4 of an ounce with each step up. Since jumbo eggs are two sizes up (large => extra large => Jumbo), you will be changing the recipe by adding an additional ounce and a half or 7-1/2 ounces instead of 6 ounces.
You may wind up with a moister batter, but it will be thicker, you may have trouble getting it to bake through and it may not have the airy quality you want.