I looked in the grub sources.  See stage2/fsys_ufs2.c:ufs2_dir, and
the assignment to fsmax.  This seems to imply that grub can handle
indirect blocks in the inode, but not double indirect blocks, but I'm
not at all sure.

Your filesystem seems to have bsize 8192, if I'm reading the
line-wrapped disklabel output correctly.

This seems to be 12 direct and 3 indirect blocks in the inode.
With 64-bit block numbers, that's 128 block addrs/block I think.
So that would be 

(* (+ 12 (* 3 128)) 8192)   3244032

Odds of an error in this is quite high.

FFSv1 appears not to do double indirect blocks either, but with 32-bit
block numbers the result should be ~twice as high.

-- 
        Greg Troxel <gdt@ir.bbn.com>