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If you put a block with a becket on the barney post, attach a single bullet block to that and another bullet block on a boom bail on the boom, you can use the split mainsheet system and have some extra purchase too. Just a thought.
A good way to do this type of mainsheet is to splice two tails(spectra is great for this) onto the mainsheet's core. While not as easy as tying on the tails, it is much cleaner(and stronger). It is not adjustable easily, however, so you might want to just tie your bridle up instead. On C-15s, we use 8:1 or 16:1 vangs that are skipper adjustable to control the leech with stern sheeting. C14.2s are raced in lighter air usually, so a powerful vang would be overkill if it was even permitted. Booms snap with 16:1s too.
With too much purchases for the sail size, you start loosing feel of the system and get alot more rope in the boat when fully sheeted in. Depending on your upper body strength, 1:1 is the way to go.
Whatever you do, don't try to reinvent the wheel when it comes to tuning tricks. Just do what the guide says and your boat will sail fast. The rest is up to you.
Sorry for all the rambling...