Concrete Saw for Trenching

Hi All,
Have just finished refurbishing an old Dembicon concrete floor saw. Has a 9hp Honda engine and can take a 14"dia, blade with 4" depth of cut.My idea being to cut a 3"-4"slot in each of 2 driveways to run pipework across the front yard for water supply, and reticulation. I also need to run a trench across the front lawn inline with the concrete cuts. Was thinking of using the floor saw with a different type of blade fitted to do the trenches?
Has anyone used a trencher with a rotary blade, are they available? Seen one on E-Bay that does lawn edging and trenching also, but these are in the USA. I was hoping to buy a dedicated blade or modify something to do the job. I could hire a trencher but the runs aren't that long and 45mins-1 hour would be enough time for the job.Thanks in advance.
Regards,
Gary.:D