A very brief update.
LiquidCrystal440 wasn't even accepted by the IDE when I tried to compile and yes I had spotted the spelling error and corrected it in the .h filename. The problem was with the deprecated expression it was using.
Having managed to get a display (of sorts) running using LiquidCrystalFast, the problem appears to be timing related to the read/write times required by the display as I can get line 1 to display, the last character of line 1 repeated on line 2, what should be on line 2 on line 3 and similar problems.
So unless I get the time (and inclination) to start a major rewrite of the library code, I'm sticking with either a single 24x4 display or possible a pair of them running on I2C addressing which I know works fine on my multi-role GPS system.
Batron did finally respond with no more information than I already had.
Interestingly they don't even make a 6 line display any more.
Dale H