Sorry to get to this topic late but has it bee specifically mentioned that Moria used TB when he got to GL? I mean, if not, then maybe he got to GL in regular ship and then decided to make TB in GL?
That isnt the problem. The problem is the red line, the 10,000 meter high 10,000 meter deep solid stone wall splits the whole op world in half. The north blue and west blue on one side, and the south blue and east blue on the other side. On the N/w side the New World runs through the center spliting those seas apart and in the S/E side the Grand Line runs through the center spliting those two seas.
Since Moria's island he was on was a west blue island, yet it was in the GL, that means it had to have come over(or under) the red line.
(If it was a south/east blue island he could just sail it through the calm belt, but since the calm belt has no wind, then i would want to know how moria rowed an island.)
So i guess what i am saying is, even if moria didnt make TB himself, who did and how did it get over the red line and how did mora find it?.
We have already established Garp's battleship is too large to make it over reverse mountain, since TB is much larger then a battleship it couldnt make it over obviously.