The problem is the clearance between the block and the sender. The wrench barely fit, my adjustables didn't. 27mm is larger than you think, the smaller ones won't open that wide.
Also as randy implied - you'll be REALLY leaning on that sucker to get it loose, so the adjustable ain't that great. Try not to smack anything when it comes loose. I don't remember what I nailed, but I remember that it hurt
Have fun!
Stef