I think you are going to need to replace those rubber hoses with a silicone hoses and the proper clamps. I would hate to lose one of those hoses in traffic . Rubber hoses aren't really meant to be used in that manner and the quality of hoses today is basically crap.
The Air flow through the radiator needs to checked too. Have you tried setting up some sort of smoke generator ( a bug bomb will work) and with the fans running watch the air as it is sucked into the radiator and where it goes when it is expelled ?
You need a lot more Air volume that you realize and the water must be able to move through the core easily. With this in mind I would install a secondary booster pump close to the radiator .A lot of modern cars have electric pumps and Davies Craig sell a pretty good Electric water pump.
A automotive water pump isn't designed to move a lotr of water against a big 'head' of pressure caused by a having to move a massive extra volume as you have with pipes running to the rear.
One litre of water weighs a Kilo,so if you have an extra 20 liters of water that is an extra mass of 20Kg. that the pump has to shift and under acceleration the relative mass is increased.
Another thing to consider is air bubbles in the system,air will not conduct heat as effectively as water.
You need to set up a bleeder close to ther highest point near the radiator. a coolant expansion tank is ideal for this if you can connect a hose from the high point to the tank to allow air to escape.
Also,a point to consider is pressure. A cooling systen needs pressure to prevent boiling. Every point of pressure increase results in one degree cooler running. Other wise at 175 your cooling system would be boiling and the temp would continue to rise . Get a hold of a pressure tester and pump the system up and examine it for leaks . rectify any of those before serious road testing commences to eliminate heartache later on.
Make sure you have the correct thermostat installed too. A cold running engine is as bad as a hot running one.