Well, at least make a phone call and ask them if they supplied you with an extra dowel. Make them identify the dowel it is meant to represent or replace. This will effectively place all responsibillity on them if it's a dowel that was left out of the build. This way, when you start the motor and it squirts oil from under the head or a piston rod disconnects from the piston head and gets jammed in the motor and beaten to hell by the rod, you can call them and it's all on them.

Just a phone call. They will tell you whether or not they need to see the motor.