Answer: A gas engine rototiller should be able to work its way through the mass of roots. You'll just have to take it slow and easy, stoping to untangle as necessary. It would be much easier than hand digging with a shovel. I don't think a sod cutter will do a very good job so stick with the tiller and start on one edge of the bed and slowly work your way down the bed. Once you get the roots out (and the weedy old grass), rake the area well to remove the debris and then plant or lay your sod. Best wishes with your new garden.
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