So, depending on how you rig the clew attachment, you might need a beefier gooseneck than have been suggested here so far. If you've got the clew attached to the boom, with the mainsheet attached at a different location, say near the boom end, then boom will experience a lot of compression loading when the main is sheeted hard. You'll need a sturdy gooseneck to handle it. Might be wise to adapt an exisitng gooseneck to work on your boom section. Here is an example of this setup:


As the main attachment is placed further aft, compression loading increases as the blocks/sheet angle to the rear beam goes well past vertical. You need some angle to get reasonable mast rotation.


If you use a webbing strap around the boom, with the clew attached above and the main blocks attached below to the same strap you can minimize the compression loading, but might loose mast rotation stability, esp. in lighter air.

Here's an example: