From the Archaeological Fantasies blog"
Firstly, the language and the lack of case sensitive modifiers used on the stone was not what one would expect from 14th century Norse. Certain words in the inscription were not in use at that time (Wahlgren 1958, Fridley1979:152, Fagan 2006:119, Williams 2012:13), however, those same words were common to the area that Ohman’s friend, Sven Fogelblad, was from (Fridley1979:153). Fogelbald was an itinerant teacher and former minister originally from an area of Sweden well known for having lots of authentic runic inscriptions lying around, and who had known and apparently studied under Claes J. Ljungstrom, himself a widely known and prominent runologist (Fridley1979:153).
Also suspect were certain runic symbols that were not known to the Futharks (the name of the Runic Alphabets) in use in the 14th century, but again these were know to Fogelbald and apparently were rather specialized to his particular region of Sweden (Wahlgren 1958, Fridley1979:152, Fagan 2006:119, Williams 2012:13).
At first blush there appears to be several versions of the Futharks at use on the stone’s inscription. However, sometime in 2004 it was suggested that the runes mimic those in the notes of an 1883 journeyman named Edward Larsson. Honestly, the only place I can find reference to this is on the Wiki and their reference is in Swedish. My Swedish is not good enough to read a whole paper, sorry. In the same paragraph the runic inscription is tied to the Knights Templar, so, take that how you will (I call it a red flag.)
Based on all this, Blegen put forward the probability that the stone had been carved by two separate individuals working together and that several individuals were involved in the hoax beside Ohman and Gran, including Fogelblad, and Andrew Anderson, Ohman’s neighbor (Fridley1979:153)."
...and...
"Blegen focused particularly on an interview done by Dr. Paul Carson, Jr. in 1976 with Frank Walter Gran about Frank’s father, John P. Gran (Blegen 1968, Fridley1976:154). The interview centered around John confessing that he and Ohman had carved and hidden the stone as a prank against “people who were really educated (Fridley1979:154).” This was significant because it was suggested that the inscriptions were carved by two different individuals, one right handed and one left, and John was left-handed (Fridley1979, Blegen 1968). "