That the Khufu boats are attributed to the builder of G1 is based solely on one cartouche, the one found in Campbell's Chamber. This cartouche is based solely on Wilkinson in the early 1800's. Since it's find in the chamber, all of these cartouches and any one similar, is automatically connected to Khufu in the 4th dyn.
That's all they have. One cartouche. Without it they would still be stuttering about the name of the builder of G1 and to which dynasty he belonged. Everything hinging on that cartouche, and that would be everything 4th dyn, is up for debate.
Not quite just the one cartouche. The southern boat pits bears the cartouche of Khufu and the name of Dejdefre on the beams which covered Khufu's southern boat-pits. Uncovered by the Japanese work crews doing the removal of the boat pits covering beams.
On the walls of the pit were several builders’ marks and inscriptions, including some 18 cartouches containing the name of Khufu’s son, Djedefre. This suggested to many Egyptologists that some parts of his tomb complex were not completed until after Khufu’s death. One scholar has theorised that the two boat pits were built by Djedefre as a gesture of piety connected with the establishment of the local divine cult of his father and founder of the royal necropolis in Giza. However, if the boats were used at the funeral of Khufu, it would have been natural for Djedefre to bury them with his cartouches.
According to Yoshimura, while the filling around the sides of the covering stone was being cleaned, the team uncovered the cartouche of Khufu inscribed on one of the blocks and beside it the name of Djedefre. This, he argued, meant that this boat has been constructed during the reign of Khufu and not, like the first boat, during the reign of Djedefre.