OK here's the contributions so far, in order received. When I get the spreadsheet going, it can be sorted and filtered by assembly plant, model year, build date etc.
Plant: LOS
Model Year: 69
Body Plate Build Date: 09D (1968)
Jack Mast Section: square
Jack Base: nothing stamped
Mast Date Code: mast, 8J
Plant: NOR
Model Year: 68
Body Plate Build Date: 04D
Jack Mast Section: trapezoidal
Jack Base: (to be confirmed)
Mast Date Code: rivet, 8D
Plant: NOR
Model Year: 69
Body Plate Build Date: 03B
Jack Mast Section: trapezoidal
Jack Base: U69
Mast Date Code: rivet, 9C
Plant: LOS
Model Year: 68
Body Plate Build Date: 02E
Jack Mast Section: square
Jack Base: nothing stamped
Mast Date Code: 8B
Plant: NOR
Model Year: 69
Body Plate Build Date: 08E (1969)
Jack Mast Section: trapezoidal
Jack Base: nothing stamped
Mast Date Code: rivet, 9G
(Note: VE3 load rest)
Plant: NOR
Model Year: 69
Body Plate Build Date: 09C (1969)
Jack Mast Section: trapezoidal
Jack Base: U69
Mast Date Code: rivet, 9H
Plant: NOR
Model Year: 68
Body Plate Build Date: unknown
Jack Mast Section: trapezoidal
Jack Base: unknown
Mast Date Code: rivet, 8D