[BossCER]

Bruin-
It can and has been done. Have a look at my gallery. It just takes money and time.
BTW- a stock Boss 9 is only 10lbs heavier than a stock FE motor. It is insignificant. It is also only 3" wider. I don't know about the weight and dimensions of the Kaase headed 385 series motor (my motor is '69 Boss Nascar motor).
The FFR guy referenced above stated that he had to put his heads on the motor with the motor already in the car. That is not the case in my situation as I have had my motor out twice through the engine compartment. The valve covers did need to be removed.
Good luck!