@DaveJ , We've been down the crane road a couple of times. The issue is that the "factory" halyards will bind with the tang that holds the forestay if they don't route pretty much down from the mast exit. Here's what it looks like without the crane, and you can see how it would intersect with the tang if extended forward to a block on the crane.

Our current version extends a solid 6" in front of the furler swivel, but also uses it's own halyard since the tang is still in the way.

This crane was welded up from 3/16 angle aluminum, bolts to the original crane mounts, and also has two bolts into the mast. It's very solid and very light. This is the part just back from the tig shop, prior to machining and cleanup.

I'll get a picture on the weekend now that the mast is back up.
The 310 is virtually identical to the 270, just bigger.
Hope it helps
Gary