everything wyotimberghost said, but one more thing....

how old and in how good of shape is your grandpa in. way easier physically in the black hills.

if you are both up to it physically, and have some muley savvy, the bighorns would be great, but remember in rifle season, especially if theres snow, look more toward the face than way high, they migrate, and get on to private land down low, so ya gotta be in their area of travel. if its warm, there will still be deer high, but again, get away from the roads.
let your optics do a lot of the walking.

never hunted the black hills areas labeled as "walk ins" but i look at everywhere as a walk in. just get away from the roads, and the number of hunters magically disappears.....

for muleys in the hills, man its tough to say any one place. i have seen too many nice bucks all over to tell one. the area around the small towns of osage, upton and sundance have lots of muleys for sure, but lots of private land too. maybe try giving some land owners a call, all they can say is no. have heard good things about the bear lodge area north of sundance, but have never hunted there myself, so cant help ya with that one.


one thing for sure, you better hurry, apps are due in cheyenne for out of staters on the 15th!