Actually...
<Product Extra Fields> mod adds another table [products_to_products_extra_fields] which holds the actual information. This is linked by product_id.
Looking through {easypopulate.php} I found 58 instances of TABLE_PRODUCTS. If I knew how, would these 58 instances be where I would add TABLE_PRODUCTS_EXTRA_FIELDS? If so, this isn't looking too good.
<Product Extra Fields (PEF)> allows new fields to be created in the admin page. And it adds the fields to the product description in the catalog. It integrates with the product add page in admin the same way <Header Tags Controller> does.
I still don't yet see a way to merge <EP> and <PEF>. The easiest way, if possible, would be to create a field (in products_description) that links to fields from the <PEF> contribution.
Anyone have any ideas beyond this?