Since I'm unemployed at the moment and bored out of my mind, I ran some quick #'s based off the manufacturers website and my own research. Heres what I found:
Using AISI 201 stainless steel for the hose clamps, assuming you are using the largest width clamp which their site says is 15.8mm, I come up with a yield strength of 686#/side of clamp in pure tension with a total of 1372#'s/clamp. Keep in mind this is a static load and doesn't account for the worm or screw gear connection. Ultimate tensile strength is 2744#/clamp. If you don't know the difference between the two after the yield strength is reached, for all purposes the clamps have failed and elongation or yielding is occuring. At that point you better run.
Now my Ford Tool (OTC 7045B) uses a 3/4" all thread rod. Im assuming a typical A36 steel but it appears to be hardened so its probably more like 50ksi. Using the 36ksi value, I got 15,900#.
So with that reasoning you would need 12 clamps to equal the strength of the tool that was made for this purpose. And again thats not taking into account the gear connection of the clamps which probably greatly reduces the values I listed.
If the strength due to the connection reduces the value by half and you use 50ksi steel for the threaded rod on the real tool, you would now need 33 clamps to match the strength of the tool Ford designed. For me, I'll just stick with the tool that was designed to do the job. My life is worth more than $300
Feel free to check my #'s, I did them quickly and didn't check them