Sizing of coolant/water lines.

[jimmy six]

I've used Jabsco centrifugal, Jegs, Maziere, CSI's and Stewart electrics with successes and short comings. Plumbing and routing are as important as the pumps with my GMC's. I've seen mechanicals work better but I never could fit one on mine....good luck...JD

[1leg]

If you must run an electric water pump we always recommend the highest flowing pump. The bilge pumps by design will give you more pressure vs. Meziere pumps but they tend to not like the hot temperatures. We typical see 21-23 gpm in a big block super gas car with a front mounted radiator and 55gpm electric pump.

I would also recommend using hard line from front to back. I would recommend 1.500" aluminum tubing. The important thing is to make sure the lines are run straight and flat. This will reduce the restrictions and any chance of trapping a air bubble.
The rad in the tank is an excellent idea and worth looking at for this project. I think it is a better idea to pressurize the system this way. Just remember in a system like this you will want to fill the system on the low pressure side. You will likely need an expansion tank to fill it properly.