Long story, I will try to be as brief as possible, dropping a '58 mercury car 312 in a '53 ford truck. I also have a 1955 dump truck motor for parts (272 or 292). I like the look of the truck front motor mount, changed out the cast timing cover, bolted in the frame piece, and bolted into truck, so far so good. Decide to use the car water pump and bolt fan to pump instead of the remote higher location.  Thought I would use the 312 harmonic balance and pulley as well, this is where I have run into trouble, it hits the motor mount. Do I have to use the truck lower pulley, does not look like a harmonic balance ? am I trying to combine parts that should not be ?, is there a difference in the motors as far as balancing, is the truck balanced at the fly wheel and not the harmonic balance ? are the crankshaft pulleys interchangeable ?