re: changing the dimensions –

It seems to me that a viable strategy would be to locate the clock mechanism you want to use FIRST before embarking on making the clock in any form.  Then get out the paper and pencil or start up SketchUp or whatever and draw.

That said, I’ve got the clock queued for starting in February when I get back from business trips and have time to DO SOMETHING!  In the mean time I have a couple of drawings started, mostly to fiddle with embellishments such as an alternate base or perhaps a touch of chip carving in the panel below the clock face (or chip carve the face instead of using a factory made one!).  Not a huge fan of Shaker furniture for the sake of being a fan of Shaker furniture.  Nothing wrong with exploring and experimenting with design.

Especially if you own a fireplace.