I should have added my calculation. Size of the block times 2 plus 7/8. (4 1/2 x 2)9 + 7/8 and I rounded up to 10"
There was very little trimming, used my Tucker Trimmer (love that tool). I should note that using this method you end up with 4 extra blocks, but I figured they could be used on the back.
https://www.youtube.com/watch?v=Vw7qi3uHUZg