Upper bunk bed size on Class b's with top bunk?

[FlyHigh]

We looked at a 97 okanagan the other day, it is just like the Airstream b190 with the large fiberglass topper. The front bunk was pretty roomy and tall and it would work fine for my 120lb girlfriend and my 150lb self. We're both in our early 30's so getting into the top bunk isn't a big issue. Unfortunately the Okanagan didn't work for us for other reasons. Now we've found a good condition 96 Ford Coachmen. Its far from us but near some family members that could take a look at it for us. Unfortunately that means we can't test out the top bunk. The topper on the Coachmen doesn't appear to be as wide as the okanagan or airstream. Anyone know how they compare? I can't find a manual anywhere. Is there an official size mentioned somewhere of what the top bunk bed size is?