It shouldn't be all too difficult to get a fairly accurate idea of the dimensions of the 978....

Assuming the phono in jack on the front is a 1/4" jack (or if one knew the dimensions of an HDMI, XLR or RCA jack on the back panel), couldn't one extrapolate the width and height by printing a large (say a photo quality print on legal paper) and measuring the overall width/height as compared to the known dimensions of a phono jack(or other). On to the hard part.

Assuming that the front panel and back panel are the same width/height, one could, with some ninja maths, reckon the depth based on the distance shown from the front panel to the back as shown on the front panel panel pic (which shows some one point perspective).

One could do this, if one were so inclined; it would be easier said than done, of course.