Accuracy of original gauges, hmmm. Well they get you in the ballpark but they are not a home run. The gauge needs to be electrically matched to the sender and after this long I don't believe anybody has original sending units. Maybe the newer reproduction units are more accurate just because they are new but because they most likely are as awful as any other aftermarket part sold these days I highly doubt they are perfect either. I'd guess you'd have to spend a lot of money on really good digital gauge sets to get any kind of accuracy.
The stacked gauges just look so friggin cool. IMHO.