UPS shipping options

My criteria are painfully simple yet extremely rare to find.

1. I need UPS to calculate price based on dimensions, rather than just weight.
2. I need to allow more than one product in a box.
3. I need to have some items ship with a flat rate.

Will Zen Cart deliver this, perhaps with some add-ons? I'm looking for a free shopping cart, haven't installed it yet, want to make sure it meets requirements and in spite of spending hours searching I have not found a suitable answer. Currently using OS Commerce but finding it lacks for combining items in shipping or having more than one shipping option only on certain products.

Thanks!

This is a shopping cart and not a intelligent box packager

Most strike a balance

If you can not create a set of conditions, it can not be automated

I'm just trying to figure out what Zencart is capable of. Perhaps someone can answer me that. I'm certain a set of conditions can be created for each of these circumstances, as I've seen some of it - such as dimensional shipping - available in shopping cart systems.