I have found if you Install all your Hardware(Rudder,Strut or Drive and Turn fin), Build the Radio Box (with Servos and Recevier and Batterys,push rods and seals)(Except throttle), Place fuel tank loosely were it will be placed, Then put your motor with it mount in between the Rails at 30% to start( I also put in Hull misc. pieces, Stuffing tube and Flex cable,what ever is left to finish hull....

Place a 1" Rod under hull or pick it up with Two fingers Directly under the center of the motor,gently and see which way the Bow or stern goes...If bow drops, Move motor back 1/2" at a time toward the transom or less until it well balance holding it by two finger directly across frim each other under the motor , or it balances on the rod under the motor. I have found that all boats are made differently, even if it is the same hull.

After you have found the right spot for the motor, Adjust it w/mount at the angle it needs to be for the type of Drive it will use, Surface or sub-Surface. Then Check it again. If all is good, Drill the holes for the mount, I normally Clamp mount and Motor into hull,then mark hole location,( Make sure if your mounting the motor as low as you can go ,to put a piece of wood? Thickness depending how low you want to mount the front( Starter) and rear of motor (Collet ) that way the motor won't touch or ride on the bottom of the hull.

This is the way that I was taught, I am sure that there are other ways that will work for others, Just my 2 cents....
Now that I have confused you, E-mail me and ask away....
Jim S