OK, just to correct a few errors....
To upgrade the front brakes you need to replace the callipers (the latter ones have longer mounts) and the dust shield (part no 47781-60100 - £64.58 + VAT).
To upgrade the rear you keep the same callipers, but need to replace the rear backing plate and dust shield as well as all the handbrake bits.
If you have access to the parts second hand it is worth doing, otherwise I wouldn't bother, you would be better off just upgrading to better disks that are going to cool better - the bigger brakes use the same pads as the smaller ones, it's just that the bigger disks cool better.
WRONG.. calipers are different, wider on the later trucks.The calipers are the same for old and new trucks. The newer ones just got bigger discs and the mounting points for the caliper moved further out giving the pads more leverage. On the front you would need swivel housings from the newer truck to bolt your calipers onto and for the rear you would need the backing plates. The rear backing plates may be the expensive part as a seller might only be willing to sell the whole casing.
If you haven't rebuilt the calipers I would do that first as you might be losing out from the pistons not moving freely. Even with the bigger discs and calipers further out the brakes are not great with big heavy wheels (tyre size makes a big difference) so before you go to a lot of trouble it might be worth getting a drive in a newer truck with the same size tyres as yours. My old 80 hated stopping
Thanks @Billy Williams and @stumog. This is exactly the kind of conflict I have found in other sources I mean it either works or it doesnt. Might be worth noting I've no abs on my cruiser although I don't think that makes any difference here.It works I did it 3years ago....
No issues what so ever
My brakes are down 25% since the last test (2016) I put this down to the new tyres 285/75 as aposed to standard at the last test. This is why I was thinking upgrading to larger disks / calipers might be my only option.Overhaul your calipers , buy new disks and change the fluid .
25 years ain't bad like