The only reason you would want to offset the motor is for clearance reasons. If you CAN put the motor dead center, than do it.
But before you weld those mounts, have you bolted on the exhaust manifolds, the steering, the radiator with the fan on the motor>
You really need to "mock" it up. My brother recently did a Model A where the motor was all installed and set up and the guy was having him finish up the car. The guy apparently never set up the motor with the water pump on! There was NO room for any pulleys!!!
Trial fitting parts is time VERY well spent.
Brian
