yes, taller front coils, different radius arm brackets, not sure about the rear suspension, possibly taller than normal lift blocks & U-bolts.
If the springs are unique to the High Rider, then it seems that the Federal Compliance door sticker should also be able to be used to confirm that a truck is a factory-built High Rider.
The truck for sale now includes the compliance label in the eBay ad. It shows a front spring code R, and a rear spring code X:
The 1988 shop manual gives these part numbers:
Front code R E77A-5310-RA
Rear code X E77A-5560-XA
The "E7", I believe, denotes 1987 model year, which makes sense if the High Rider was first made in '87.
There are only 6 rear spring options shown in the shop manual, and there is only one "E7", the other 5 all being "E6".
But there's 21 codes for the front springs, running from "E2" through "E7".
I don't think that I have anything else in my lit collection to further confirm this. The Ford truck parts catalog might break down the part number suffixes (i.e.- RA, XA) into applications or specifications, but I don't have a complete copy.