So, you're going to have approximately .630 in. open space between the back of your hub and the front of the engine??? What you are doing should work fine on the test stand where the only loads that your turned flywheel center section will see are torque loads. OK, for the loads on your center section you have to add the front section of your prop hub (moment arm), then you need to consider the gyroscopic loads (bending) of a 16 or 17 inch prop plus the moment arm. You are going to be putting a lot of stress on a very small area of CAST ALUMINUM that was designed for torque loads only when you are actually flying this setup. Just my opinion, others may disagree. Good luck with it.