Lag screw question:

[NYC_SKP]

7. If it's truly a 1.25" shaft diameter lag bolt, you should have no problem.

If I picture the situation correctly, you've got 4.5" of bold shaft extending from the trunk, 1.5 of which is the thickness of the two-by, plus the three inch space.

So you have a cantilever which may tend to bend the bolt under a heavy load.

If you can bring the 2x12 up against the bark, then you've reduced the moment arm of the cantilever and multiplied it's resistance to bending.

Is there a way you can encourage the 2x12 to meet the tree and get a spacer between it and the hex head of the lag?

I've got to say that I don't think I've ever seen larger than a 3/4" lag, good job in finding a monster fastener!