hos327,
The dimensions of the 1M rack are as follows:
16-1/2" W
13-1/4" L
4" H(front of rack)
5-1/2" H(rear of rack)
IMO, an easier to install/cleaner looking finished product may be to go with a M-series style rack. With this particular syle rack you can adjust the length size to your specific needs since the front and rear rack are independent from each-other.....
Hope this info helps...
-John