First make the giblet broth. This can be done ahead of time.
Heat oil in large heavy-bottomed saucepan over medium-high heat until shimmering but not smoking; add turkey neck, heart, and gizzard and cook, stirring occasionally, until browned, about 5 minutes. Add roughly chopped onion and cook, stirring occasionally, until softened, about 3 minutes. Reduce heat to low; cover and cook, stirring occasionally, until turkey parts and onion release their juices, about 20 minutes. Add chicken broth, water, and herbs; increase heat to medium-high and bring to boil, then reduce heat to low and simmer, uncovered, skimming any scum that rises to surface, until broth is rich and flavorful, about 30 minutes. Strain broth (you should have about 8 cups), reserving heart and gizzard; discard neck. When cool enough to handle, remove gristle from gizzard; dice heart and gizzard and set aside.
Melt butter in large saute pan over medium heat. Saute the diced celery and onion until tender and translucent, but not brown. Remove from pan.
In the same pan, saute sausage until no longer pink, breaking up into small chunks.
In a large mixing bowl, combine all the above ingredients (heart and gizzard, vegetables, sausage, apple, eggs and parsley) with two ten ounce boxes of Mrs. Cubbison's STUFFING (not dressing.) Gently stir in 2 1/2 cups of the giblet broth. (Reserve the rest for gravy.) Add more liquid if needed. Bake for 45 minutes at 350°F.