He he, cheers gents.
Well the results just in, it's simply a case of adding the additional files in the truck download into to relevent folders in the original 8.3 setup. There are some folders and files that are not in the original directory, just add these. And there are some files which are identical, you'll get asked if you want to duplicate or replace, just replace.
After a few niggles, it fired into life
BUT......... I've set up 3 profiles for trucks I use regulary, one 6.5 ton 8 foot high, one 26ton rigid thats 12 foot high and one 150 ton artic (well technically a locomotive :)) thats 16 foot high.
Then I set some routes, with the start and finish either side of known low bridges or weight restrictions.
No matter which profile I select, the route takes me under the low bridges or over the 3 ton weight limit, which is a bit worrying.
So needs some more tweaking somewhere.
I'm working tomorrow so I've taken the truck back off the SD card, so I can get used to using the new sat-nav tomorrow. I'll get another SD card and load the truck onto that, so I can swap between the two quickly, that way when it goes quiet at work I can experiment with the truck setup.
Also with the truck, the whole map is surrounded by option/menu buttons, it's quite confusing and will need a while to get used to it. The original 8.3 is quite simple to use,
So, so far so good, it was just a case of Who Dares Wins :) :) , I'll experiment more with it later.
I'm writing everything I do down, and when I'm happy I'm planning on posting up a complete Eejits guide to installation, should help people in the future.
Cheers gents :)