Perhaps for the food in which you feed chicken backs you can use this calculator to determine proportions?:
A calculator to create recipes for feeding dogs raw meals. DIY Raw Dog Food Helper.
www.rawdogfoodcalculator.com
For bonemeal, assuming that yours is the same brand referred to in Karen Beckers books, you can refer to these tables:
The tables are specifically for the recipes in her books, where she feeds either chicken, turkey or beef. But I think boneless meat doesn’t contain calcium and there is marginal differences in phosphorus. Maybe you can see the difference between the pork you are serving and adjust accordingly.
If I’m not mistaken, adult dogs can regulate how much calcium they absorb in calcium rich diets, so slightly more calcium may not be a big deal (anyone feel free to correct me if I’m wrong)