The long shoe was offered in 1990 models, but could be put on older ones. The Cross-Flow fan can also be adapted to the 1680. The 1680 is a good machine that will definitely outcut a 1480. The cab is certainly better than the 1480. We had the long shoe and good fan and it would run circles around the 1480. We were using a 24' foot 810 header (a holdover from the 1480 that the 1680 replaced), though, so your results may vary.
That being said, our 1680 was an '88 model (Granddad bought it used) and it was sort of a problem child, starting with a connecting rod that decided it didn't want to be in the engine anymore. I think it had the old DT466, though. Our dealer put in a 8.3 Cummins and we never had any problems with it (the 8.3 was used in '89 and up models). We seemed to have a lot of problems with the bin unloader drive. In corn there was a tendency to break shear bolts if the unloader was engaged too fast. I know there were a couple other issues, but I can't think of them off the top of my head (it's been a year since I've ran it).
I know in '89 they beefed up a lot of the components, which should solve the little things that always plagued us. I would have no problem recommending an '89 and up 1680. If it doesn't already have it, put in a Cross-Flow fan. It's worth the money. I think a 1688 might be more reliable, but in my area they're hard to come by. A 1680 that's well taken care of should be a good machine.