I have the one of the original Weber Grill cookbooks, called
Elegant Fare, from 1977. The directions they give for roasting
a whole turkey are based on their recipe for roasting a whole
chicken (just bigger, I guess). I will post the roast turkey
info first, followed by the exact text for roasting a chicken.

Roast Turkey

3/4 to 1 lb - turkey under 12 lbs = 1 serving
1/2 to 3/4 lb - turkey over 12 lbs = 1 serving

To prepare: See roast chicken. When the bird is trussed, rub
with peanut oil. Insert meat thermometer in center of inside
thigh muscle.

Roast Turkey Cooking Chart

Roast by indirect heat method for charcoal, by indirect heat
method (low heat) for gas, breast side up. "Baste frequently."
Roast to internal temp of 180 deg. F. Allow to stand 20 min
before carving.

Estimated total cooking time

For stuffed turkey, allow 13 min. per pound
Fresh or Frozen,
thawed Int. temp Time
6-8 lbs 185 2 to 2 3/4 hrs
8-12 lbs 185 2 1/2 to 3 3/4 hrs
12-16 lbs 185 3 1/2 to 4 hrs
16-20 lbs 185 4 1/2 to 5 hrs

To prepare: Wipe the bird inside & out rub the cavity with a
cut lemon to freshen. Sprinkle inside with salt & pepper &
tuck the wings back. Allow to come to room temperature. If
serving unstuffed, the cavity may be seasoned with 2 T. butter
and a selection of aromatic vegetables and herbs of your choice:
Try crushed garlic cloves; onion wedges; chopped carrots; celery
stalk; apple; parsley; rosemary; tarragon; thyme. The vent of
the stuffed birds may be sewed or skewered shut. Truss the bird
tightly & rub with 1 or 2 T softened butter. If self-basting is
desired, lay slices of bacon across the bird.

The best way to describe the indirect heat method (without the
diagram, which makes it much simpler) is based on the diameter
of your grill in inches. Basically, you place your briquettes
on either side of a charcoal rail, which holds the briquettes in
place on the sides of the grill. Otherwise, pile them very care-
fully on each side in the grill so they are not directly under
the item you are cooking. If your grill is 26 in diam. use
30 briquettes on each side for the first hour & add 9 briquettes
to each side every hour. 22 3/4 in. diam, start with 25
briquettes on each side for the first hr and add 8 to each side
every hr. 18 in. diam. start with 16 on each side the first hr
and add 5 to each side every hour. DON'T FORGET to add the addt'l
charcoal every 60 min.

You can place a shallow drip pan inside the charcoal rails, if
you have them. Otherwise, I improvise & create one from double
thicknesses of heavy duty aluminum foil. It's not as sturdy,
but it does serve the purpose.

Make sure the coals are well lit (grey ash has formed on them).
It takes about 25-30 min once they are lit, to get to that point.
And make sure the top grill is positioned with the handles
directly over the coals to allow the addition of extra charcoal
as needed. Use a meat thermometer because heat in a grill is
not an exact science, so your cooking times can vary from what
is stated.

I hope this helps, good luck. And you know, if worst comes to
worst (or wurst!) you can always call your dad long distance.