I thought a mac weighed close to the same as a 28mm dd motor such as the amped one. Might be a tad lighter, so your new bike will weigh 78 pounds. Not scoffing the motor, just saying it's not a flyweight motor like a 200w type. And even those weigh a bit, full of copper as they are.
A different rack could help, do you have a wheel hold rack or a hanger type? I found the swagman hitch rack easy, I can put bikes on mine one tire at a time, lifting only half the weight at a time.