Monkeyblair, I can easily access the Forth and Clyde, and Union canals from Grangemouth, so I can go either,
Up Inchyra Road, through Laurieston, through Hallglen onto Union canal, turn left and follow the canal through Polmont to the far end of Linlithgow, down the back road to Bo'ness and head back to Grangemouth,
or
As above to the canal, turn right and head along the canal to The Falkirk Wheel, drop down to the Forth and Clyde canal, head out to Bonnybridge/Allandale/Cumbernauld (depending on how the legs hold up) then head back along the Forth and Clyde to Grangemouth.
edit to add, I've just realised that you don't live in Bo'ness, but I'm sure you know the area.