Did the road shown in the Locke guide follow US 70 or the Old Military Road west of Blackfish Lake? The post about Patterson above would seem to indicate a route along the Old Military Road. There is also that big jog shown at mile 40.9 (17.1), five miles west of "Patterson", and goes south 0.4 miles. US 70 doesn't ever seem to jog anywhere for quite some time after Blackfish Lake. However, the Old Military Road goes through a series of south and west steps, ending up in Widener where it rejoins the Dunn guide path.
I found evidence from multiple sources that there was a ferry on Blackfish lake where the Old Military Road crossed (such as
this site which details the history of the Old Military Road and its use in the Trail of Tears). The ferry was established in the 1830s, run by William D. Ferguson. In 1836 and 1837, he tried to get permission to build a toll bridge, but the request was denied. Was there ever a bridge? As late as 1892, a source says the crossing was via "an old rickety flat-boat", but this was an account of Civil War movement. An 1891 Arkansas Acts journal has the following:

Notice the phrase "to the west end of the bridge across Blackfish Bayou on the Old Military Road in Section 15, township 6 north, range 6 east...." That's exactly where the ferry/bridge site is shown on the map below. The US 70 bridge is in Section 16. So evidently there was a bridge there. However, I can't seem to find any other reference to it, and there are no older topo maps.
The road described above seems to be the US 70 path up to Blackfish Lake. Then it goes along the road on the west side of the lake, up to the bridge. So, evidently, that part of the US 70 path is pretty old. There's still the "Patterson" reference to consider for the Locke road path, however.
Here's a map of the area with notes.
