I hope that the OP's question has been answered. However, for my two cents....
When I had my home wired for my 10KW PTO generator, I had a licensed electrician do the work, When I queried him about those 'mechanical' interlocks, his reply, "They only work if and when the panel cover is installed !" If the cover is off, all bets are off.
He gave me two options. A set up where certain circuits to a separate panel are powered by the generator and a setup where the whole house was connected using a double throw switch between the power company and the Generator. For the prices that he quoted, I went with the 200Amp double throw connection. When the connection is in the 'UP" position, I am connected to my UTILITY Company and full power. When the connection is in the "DOWN" position, I am running off the limited output of the 10KW PTO Generator. Either way, all household circuits are covered. I just have to decide what is the most important and not overload my generator. As a precaution, when I am running the PTO generator, I shut off the breakers for my two biggest energy hogs...the Stove and Clothes dryer. If I do not, the circuit breaker on the generator will shut it down. I have been running this way for nearly 18 years and have had absolutely no problems.
The really nice feature with my setup is, if I ever want to upgrade the generator that I do have, when I connect a larger generator, my setup is all wired to take advantage of any increase in power.
Photo 5621a showing:
#1 - Power from the UTILITY to the double throw Transfer Switch.
#2 - Power out from the double throw Transfer Switch into the house
#3 - Power from the PTO Generator into the double throw Transfer Switch (white is #6 AWG ground for the PTO generator with heavy duty battery clamps on each end)
#4 - Double throw Transfer Switch box
Photo 5622a: showing double throw switch for either ON LINE (Utility power) or ON AUX (PTO generator)