I'm not seeing anything bizarre from the 1798's surfaces, honestly. Looks like the piece had a lot of crud on it, was improperly cleaned, scratched/tooled a bit as part that process (particularly around the rims, where that combined some leftover crud gives an odd appearance to certain features/lettering), and has generally been mishandled a bit. The central relief of this piece looks honest to me.
Gallienus, the blob of extra metal on the R in REX... Someone else can chime in regarding what actually causes that. However, it is a common occurrence on the middle years of the Mex 8R of Charles IIII... both on pieces that are fairly well believed to be legit Spanish originals, but also on swamperbob's later bullion restrikes (which he's explained in multiple posts in this subforum). Point being, extra metal like that on this type doesn't particularly brand it as a modern numismatic cast/fake.
Now, the edge pattern... a bit sloppy. Bob has made points in posts about various traits he's observed on different types of bullion restrikes... with a main theme of anything with non-"perfect" circles can almost automatically be deemed NOT a Spanish original. Defer to him for any specific expert commentary on what we have here. My
Two Cents is that I've seen plenty of pieces with normal, textbook edge patterns, but also many Charles III/IIII Mex 8R where the edge pattern is basically a mess, yet the piece can NOT be anything but "old" based on the surfaces, patina, and overall character of the coin. Now, whether "old" means an original 1800-ish Spanish original, or a later 1800's bullion restrike... another story. However, the point - sloppy edge is not particularly indicative of a modern fake.