Special color, LTD badges on the side covers, Gold rims, that's about it.
Copied from Goldwingfacts.com "Goldwing History" pages:
In the meantime, 1976saw the standard GL1000 unchanged, apart from a badly needed grease nipple on the driveshaft. A limited edition LTD model was rolled out alongside the standard model and the LTD had some nice badges, pinstriping, a better seat, flared mudguards, gold coloured wheels and spokes and some more nice but otherwise unimportant cosmetics, all at a fairly hefty extra cost of course. The LTD version of the GL1000 was only available for that one model year.
I can only go by mine and what a couple other LTD owners have verified. The carbs and rear end are numbered differently and are LTD only. My LTD is just plain smoother than my other 76s, with better transition though the range of speeds. I've had my carbs apart and they are different in small ways, if I recall the float is smaller and I imagine the jetting is different.
I think Honda wanted thier range leader to run just a bit better than the slightly smoggy 76s. I have Randak's jet mod on my yellow bike and it's still not quite as smooth.
Odd things are different too, more chrome, the Honda emblems are a different size. I think they were the test for the next year's bars as those asre different.
They claimed the engines were hand assembled for the LTDs, but I bet they just pulled some good ones off the line, there are always some better than others on the dyno.