import arcpy, os

#Map document stuff
CurrentMXD = arcpy.mapping.MapDocument("CURRENT")
CurrentDF = CurrentMXD.activeDataFrame

#Output map directory
Output_dir = "C:temp"

#Iterate through layer names
LayersToExport = ["1938 HISTORICAL TOPOGRAPHIC MAP","1940 HISTORICAL TOPOGRAPHIC MAP"]
for LayerName in LayersToExport:

    #Get current layer, make visible
    Layer = arcpy.mapping.ListLayers(CurrentMXD, LayerName, CurrentDF)[0]
    Layer.visible = True

    #Change title text
    TextElement = arcpy.mapping.ListLayoutElements(CurrentMXD, "TEXT_ELEMENT","TitleText")[0]
    TextElement.text = Layer.name

    #Get output JPG filename, remove existing, export
    Output_jpg = os.path.join(Output_dir,LayerName+".jpg")
    if os.path.exists(Output_jpg): os.remove(Output_jpg)
    arcpy.mapping.ExportToJPEG(CurrentMXD, Output_jpg, resolution=300, jpeg_quality=95)

    #Make layer invisible again
    Layer.visible = False

>>> import arcpy, os

#Map document stuff
CurrentMXD = arcpy.mapping.MapDocument("CURRENT")
CurrentDF = CurrentMXD.activeDataFrame

#Output map directory
Output_dir = "C:Temp"

#Iterate through layer names
LayersToExport = ["1943 HISTORICAL TOPOGRAPHIC MAP", "1951 HISTORICAL TOPOGRAPHIC MAP", "1968 HISTORICAL TOPOGRAPHIC MAP"]
for LayerName in LayersToExport:

#Get current layer, make visible
Layer = arcpy.mapping.ListLayers(CurrentMXD, LayerName, CurrentDF)[0]
Layer.visible = True

#Change title text
TextElement = arcpy.mapping.ListLayoutElements(CurrentMXD, "TEXT_ELEMENT","TitleText")[0]
TextElement.text = Layer.name

Output_pdf = os.path.join(Output_dir,LayerName+".pdf")
if os.path.exists(Output_pdf) : os.remove(Output_pdf)
arcpy.mapping.ExportToPDF(CurrentMXD,Output_pdf)

#Make layer invisible again
Layer.visible = False