3.33 T, divided, like so: 1.3 T for the cavity, 2 t for each breast half, .5 t for each leg and each thigh. Unlike with chicken, the salt needs to go on the flesh, under the skin. 24-48 hours, wrapped tightly in plastic.
Since having a brief discussion with Rita on this subject in one thread or another this past spring, I've played with this more, basing my forays on a CI piece, Roger's work and an interview or two, and sundry Net sources. My opinion:
For turkeys, it's essential to use kosher salt (it is much easier to spread evenly, which is necessary) and it's essential to salt the flesh directly. To do this, one must separate the skin (carefully, so as not to tear), starting with the breast side and doing so sufficiently so as to be able to reach the leg meat; and then separate the skin from the back, in order to have access to the thigh meat.
(For small chickens, especially the very small chickens I prefer, skin separation to that sort of point is a PITA and not worth bothering with. Salt the outside, the cavity, and leave it at that. For larger chickens, it's up to the cook. It does shorten the brine time but I'm not sure it's worth it. Kosher should be used if doing an under-the-skin thing for the reason noted above. For salting chicken on the skin instead, either fine salt or kosher works but I think fine is more effective.)
Salt the cavity. Next: Salt the flesh of a leg and breast half on one side first, then the leg and breast half on the other side, then flip the bird and salt the flesh of each thigh. Apply as evenly as possible and massage the salt further to make it as even as you can. Wrap with plastic wrap tightly and fridge the bird.
(The same goes for chickens. If applying on the surface instead of under the skin, simply portion the salt for the cavity and apply, place the remaining portion of salt in a small empty salt shaker, lay out a piece of plastic, then, holding the chicken in one hand backside up, sprinkle the salt evenly over the back and thighs. Place the chicken breast up on the plastic, evenly sprinkle the rest of the salt, wrap and fridge.)
After removing the turkey from the fridge, rinse it well, lifting th skin to let water flow under it. Remember to rinse the cavities. Drain well, then pat dry inside and out with paper towels.
(Same for chicken.)
Err on the side of caution and make your gravy base (if gravy is on the menu) lightly- or no-salted. Adjust salt after finishing the gravy.
It might be worth practicing this once or twice with a chicken before doing it with your expensive heritage to see how you like the approach and to make any adjustments you feel necessary. Get a larger chicken so that the skin thing is easier to do (it's much easier on a turkey). Eyeball the package before purchase to make sure the skin is fairly intact as commercial chickens so often have damaged skin.
The salt proportions are the same 1.25 t DC kosher per pound of chicken. (A scant 1 t for Morton, a scant 3/4 t of fine sea salt if salting a small bird on the surface.) Portion the salt for the cavity and each part of the chicken's flesh appropriately, using the guidelines I noted above for your 8-pound heritage, and give it a shot.
Not cooking the big dinner this round so ordered a heritage to experiment for a smaller family dinner at home. I was really thinking of buttermilk brining but that seemed like something folks would advise against as it would hide subtle differences in the flavor vs a "robo" turkey. Figure I'll start with straigh salt/water brine may flavor a little not much.