First off: I don't have G-cat and have never even been near one!
Boomless advantage is you don't get hit on the head by the boom when you experience your first involuntary gybe. In stead you might (for example) just get rope burn from the main sheet.
A boom's main advantage is that it gives you more options for trimming the main sail. Note: that includes options for trimming the main badly. These options by far outweigh the few options for trimming the main properly. Incidentally, my boat has a boom, which I like very much, but it's no holy grail.
I could be mistaken ( I don't know how a Louisiana G-cat should be rigged) but the mast is usually located on the front (or main) beam (in the middle). One hole on each cap would normally be for the trapeze bungee. Some boats contain integrated righting lines there, but I couldn't say if yours was one of them.
Check out the link below for some pictures of a rigged Nacra:
http://www.thebeachcats.com/index.php?module=pictures&g2_itemId=35563Note that not everything will be exactly the same, but a lot of stuff should start to dawn on you if you just stare at the pictures long enough.
Good luck (You'll need it!)
Dennis
