That's going to be tricky since gantry is a 1200px (large display viewport) 12 column grid. - therefore each of the columns is one 12th of the overall template size. 1240 is not divisible by 12 (with a whole number), furthermore using that columns layout is likely to yield tiny columns in a responsive template any (tablet and mobile) so again it might not meet your needs.
also 12 is not divisble by 5 (each position has to be a whole number of columns) therefore again this is going to give you issues. Especially trying to get it working in a responsive layout (5 viewports).
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