Ore cars for HO

I’m building a shelf layout in HO and eventually want to replicate a coal mine in my area, it’s a slope mine, the cars come out of the tunnel slope and are switched back to a tipple to dump their load. I want to scratch build the ore cars onto wheel trucks but am wondering what size would best fit HO, the N or Z. I would also hope to scratch build over a motor chasis to push the ore cars up the slope. Any thoughts on the best gauge to use please.

http://www.comstockcarshops.com/MINING%20PRODUCTS.htm

This might help.

Check out my post today “Old Time Figs & Bldgs”. This site has a lot of different cars & figs in both HO & N scale.[8D]

Thanks to both of you.