My understanding of why the water goes IN at the TOP of the radiator is because if air is introduced, or water escapes from the system, you will always be circulating water if drawn from the bottom of a partially filled radiator. Other than that, an airless system (does such a thing exist?) shouldn't make much difference on a forced-flow system. I'm using the electric pump, with water flowing in at top of radiator, out at bottom, and into the heads first (which I would promote with any motor), then out of the block, with the water pump pushing directly into the heads to insure the least amount of pressure drop before it enters/exits the motor. I've never had a heating problem...yet. BTW, the radiator I'm using is a typical single pass, 3" X 26" x 15"core. The shrouded fans only come on if no forward movement airflow exists. The aluminum ducting is sealed around the radiator to the point where very little bypass airflow exists, thus all inlet air/ram air must pass through the radiator.
I used well-nuts to mount my radiator (which uses side plates much like you're using) to isolate the radiator from a solid mounting configuration only due to a concern of chassis flex transfering to the tank/core bonding.