I found the EIS's for the late 90's plans for the US 61 bypass of Hannibal in Northwestern's Transportation Library today; the EIS said that US 61 was to be upgraded to freeway south of Hannibal, and freeway upgrades were apparently being strongly considered for US 61 north of Hannibal. The westernmost alternative ended up being chosen. IIRC, the southern endpoints for all of the considered routes were near Route M or Trabue Lane; all of the northern endpoints were at the US 24 interchange or at US 61 east of US 24.
The library also had the 1990's EIS's for MO 141 between I-44 and Clayton Road. There were apparently two corridors from the 1970's that were no longer useful due to housing developments, with one being a western route near Sulphur Springs Road that intersected I-44 between current MO 141 and Williams Creek. The eastern alternative was near Weidman Road and intersected I-44 between current MO 141 and the Bowles Avenue interchange with a "Scissors interchange" that I believe was described as fully directional. Unfortunately, there weren't any maps for these corridors.
As for the more modern MO 141, pretty much the only alternative considered was around the Big Bend interchange, with the alternative staying closer to then-existing MO 141. The interchange with Big Bend would have a diamond ramp setup for northbound traffic and a folded diamond setup for SB MO 141.