Some years ago there was a crazy science exhibit going around museums in the US that had human cadavers preserved with some plasticizing process where you could see different tissues. They also had cross sections.

They actually had an exhibit showing the effects of obesity on tissues. This was before fat acceptance became a thing. That was really an eye opening exhibit showing shrunken muscle tissue, shrunken hearts, shrunken/squeezed lungs, etc.. in obese people.

Kind of opened my eyes as to how crazy the changes are.

You're describing it backwards.

Obesity tends to cause heart enlargement (https://radiopaedia.org/articles/obesity-cardiomyopathy), larger muscles (as you're doing essentially built-in weight training just walking around), and organs don't tend to shink; cross-sections show a pretty similar body cavity (https://www.cultofweird.com/medical/human-body-slices/) - the fat largely goes on top of it.

It was a really great exhibit, watch a smoker regret his life choices in real-time when given the chance to hold a lung taken from a smoker.

I believe you are thinking of 'Body Worlds' [1]

[1]: https://bodyworlds.com/