I haven't seen anything like that. I understand the appeal, I would like that option too. But by cutting into the camper you may be compromising the integrity of the camper's frame, weakening the unit as whole.
Have you considered the Blazer Chalets and maybe upgrading some of their features? I like them a lot and even their dated color schemes are kinda retro now. That concept has a loyal following and a knowledgeable owner base still out there.
Chinook camper bodies are still out there and can be added to a 90's Toyota truck. The Chinooks would likely need some upgrading as well. Comments I've read regarding camper bodies permanently fixed to a cab & chassis, expressed concern & doubts whether it would be flexible and/or rigid enough to withstand the rigors of off-road travel.
Those were just opinions. I have yet to visit with anyone who has owned and traveled extensively off-road, with a fixed cab & camper combo.