You're asking for a custom part. I have always had to provide a supplier with an exact specification for those parts with dimensioned drawings (you're to be forgiven if the drawing isn't cad quality).
My observation with the Fluidyne on my Roush 427IR was that the radiator had excess capacity and over-cooled the engine, that is, the engine ran cooler than I would have liked. Now there's probably a combination of effects including fore and aft fans and the
oil cooler that contributed. I eventually put a smaller thermostat in and the next season would have either bypassed or put a thermostat on the
oil cooler as well. The message here is that it's easy to over-specify the radiator.
My first Fluidyne developed some very small but annoying leaks in the upper right quadrant. Nothing dripped and I never really lost fluid but they were "weeping" and built up a crust. This was as I was told by some experts, due to electrolysis. So my second radiator included a "sacrificial anode" (yes, exactly like your water heater) AND instructions to ground the radiator to the chassis. Be sure to include the mount for the anode (it was at the top with the drain petcock on the bottom) on the opposite sides of the main inlet/outlets.
So what is wrong with the Fludiyne?