Yeah! Only one day, and it works!!! (I had to focus on my live site for awhile, and just got back to working on this...)

It took me longer to uninstall the Additional Products Fields mod than it did to create fields using this method!

I made one mistake that I caught and thought I'd share, just in case somebody else has the same problem. When I finished all the instructions, I had the fields in the product pages in Admin & could enter data, but they didn't show up on my site in my product info display.

It turns out I'd tried to use the override system in a place where it doesn't work. I knew you couldn't use overrides in the admin section, but usually should in the storefront section. I tried to use zen overrides for includes/modules/pages/product_info/main_template_vars.php
When I was trying to figure out what went wrong, I remembered that there was one section of the storefront that doesn't accept overrides either, and I thought it might be 'modules'. Sure enough, when I modified the file in its original location (no overrides), my new fields showed up on my site!

Now, one question for the zencart team. I noticed when I was in phpMyAdmin that if I removed the 'auto_increment' condition from products_id, it looked like I could then enter my own values for product id (I'd like this to be my sku's). Would this mess up other functions in zen if I did this? Would the answer depend on if the skus are integers vs. alphnumeric? That's all I wanted in the first place, was to use my skus as the id's.

Thanks, if any of you guys (zen team) are reading this!