Question about meat to fat ratio

[Dave]

Most recipes call for a an 80/20 ratio.

The pork shoulder should be pretty close to that ratio already. 5 pounds of shoulder along with your venison would give you 19 pounds of meat and 1 pound of fat. 20% of 19 is 3.8 so you could add 2.8 pounds of back fat to get to the 80/20 ratio.

Or you could just be a rebel and add all the fat and then let us know how they turned out.