O.k. I looked at the ACA itinerary. If you can swing it and don't mind the climbing, the day from Rapid City to Deadwood via Nemo Rd. is really nice. Here is the route I did continuing on to Spearfish:https://ridewithgps.com/routes/8788873
The portion between a little after mile 34 and a little after mile 36 is a quiet, gravel road. Once you get to the summit around mile 38.7 it's a cruise into Deadwood. Just before you start that climb there is a private campground with a "burger shack" open to the public. The burger was pretty good. Since I didn't stay in Deadwood I didn't look for camping, but I remember seeing this place. Not sure if it offers tent camping:http://daysof76.com/?/days-of-76-campground
This was my second day, from Spearfish to Hill City:https://ridewithgps.com/routes/8789073
Spearfish has the most amazing municipal campground I have ever seen. And it's right next to a national fish hatchery museum, complete with "tanks" full of fish. The gradual climb through Spearfish Canyon is really, really nice, as is the mileage to Cheyenne Crossing. When you turn on to U.S. 85 is where things get ugly. It was only 3 miles, but that climb was a beast. The sun beating down on me didn't help. Mil3 30 in Edgemont is where I picked up the trail. as you can see, there are two sustained uphill sections. Between the surface and the breeze and me being tired from the early climbing, those sections were harder than I thought they would be. Note that the only place to get any food along this stretch is at a restaurant in Rochford. Pretty sure it's not open on Sunday.
I finished the trail on day 3, passing through Custer and Pringle:https://ridewithgps.com/routes/8789263
I don't know whether the ACA trip will get off the trail at Pringle and take U.S. 385 to Hot Springs or stay on the trail until it crosses U.S. 18 and taking that to Hot Springs, but from the days mileage, I suspect it's the latter, which is what I would do. U.S. 18 has a wide shoulder and is pretty tame except for that mile or so hill you have to climb before cruising down into town. The ACA trip is going to stay at a place that's just to the north of the center of town. I stayed at a place that is closer to town on the south end. Pricey ($30) for what it was, but it is convenient and there is a lot shade. It's small, so you might want to look into tent site reservations:http://www.gwtc.net/~allenranch/index.html
This was my day from Hot Springs to Custer via Wind Cave N.P.:https://ridewithgps.com/routes/8801424
If you looked at my photos, the bison shots were all taken on this day. The nice thing about it being short is that I had plenty of time to one of the longer tours of Wind Cave. Definitely worth the $12 or whatever I paid for it. Get there pretty early or you may have to wait for a tour. When I got done mine the wait for the more popular tours was about 1.5 hrs. Bring food as once you leave Hot Springs there is nothing until Custer. Just before mile 26 on my map I got off SD 87 and took Lower French Creek Rd. That's another gravel opportunity. Very quite and scenic back there. While the map doesn't show it, there is a tail spur extension that goes out to Stockade Lake from Custer. I stayed on the road and was glad I did. There appeared to be some short, super-steep section on the spur. The place I stayed was a bit outside of the center of town. While spending three nights in Custer I saw this place, which had a shaded tent area and is within walking distance of the main drag:http://www.fcrvpk.org/index.html
Despite being close to things, it's still pretty quiet back there. One possibly negative is that I looked liked it could be a bit buggy, especially being so close to the creek.
That's all for now. I will update with my thought about Needles Highway.