bubba,
Sardis Rd. is a long one, runs through Bauxite, Ar and Mabelvale, AR. The sharpest curve I see is right outside of Mabelvale going WSW.
From what you've said about the boys lying in the road when they were struck by a pick-up truck, it sounds to me like they were likely already deceased when placed in the road. That of course would mean they had been murdered, and with the hope their being struck by a vehicle would hide that fact. As someone else said earlier, it is very reminiscent of the two boys found on the tracks in 1987 IIRC.
Who in your family identified the body of your uncle? Your grandfather? How did he determine the body was your uncle's? Was the identifying person only allowed to look at your uncle's face or did he view the entire body? The reason I ask is if there may have been other injuries your grandfather or whoever identified your uncle saw, and that perhaps didn't fit with your uncle being run over.
Where did you hear about the boys being in burlap bags? Was that from a newspaper article or from family sources?
I'm having trouble with the 3 hour interlude between when the boys were run off, and when they showed back up at that house. That's a significant time lag.
If they had been run-off as claimed, they would have had two thoughts on their minds, one seeing if they could get someone close by to help them, either by loaning them some gas or by calling their parents to bring gas for the car. How much time would they have spent trying that angle? They also might have been thinking about catching a ride into the nearest town in hopes of getting gas, that is if the car was truly on empty. It seems more likely to me that they would have returned to the car much sooner than 3 hours. They were teens, and teens do things in a hurry. If they were able to get no gas, then why would they even come back to the car? Most likely they would have just tried to hitchhike back home, and deal with angry parents, and then go get the car.
If the car still had gas in it when it was picked up from the wrecker service or whatever lot it was towed to, then one possibility may be that the boys were acting as mules, trafficking drugs for someone, and were shot once they'd completed the task they were assigned or that they'd witnessed a drug drop, and were shot to keep them silent. Then the whole story of them running out of gas was entirely made up. Of course there could be plenty of other explanations, and at this point, it's pointless to speculate. However, I see nothing to suggest this was a simple accident. The burlap bags alone, negate that altogether.
You can order a copy of the death certificate from the state of Arkansas on line since you're a relative.
I guess it all boils down to how serious your relatives are about getting answers or if you are the one pushing them to ascertain the answers. If, the latter, at some point they're likely to clam up, not wanting to dredge up their feelings, and possible feelings of powerlessnesss to do anything about it at the time.
If OTOH, they are totally serious about getting to the bottom of it, at some point, but not just yet, they may need to think about exhuming your uncle's body. If as you say, no autopsy was performed then someone had a hand in preventing it from being done, and it was prevented for a reason. Maybe an autopsy would have revealed stab wounds or gunshot wounds in addition to injuries sustained by being run over.