gridworks Mystery Cache

When sagelily and I first came upon this puzzle we stared at it for a long time before she finally worked out the key to finding its solution.  Even then, it took us a few hours to get everything in place.  We expect the puzzle meisters out there will spend far less time on this.

Place all 12 shapes on the grid, governed by the following:

• no shape may touch another, not even corner-to-corner;

• the shapes may be rotated or flipped over;

• the numbers outside the grid refer to the number of consecutive white squares in that column or row, each separated by at least one coloured square.

For example, in the first row, the numbers “3 1” mean that row contains, somewhere along it, a strip of 3 white squares (from a shape) followed by a “strip” of 1 white square, separated by at least one coloured square.

When you’ve correctly placed all the shapes on the grid, sum all the visible numbers in the mauve squares and call this ABCD.  Sum all the visible numbers in the green squares and call this EFGH.  The cache is at N45 1A.BCD W75 4E.FGH.