I don't have a lot of experience (none really) with prototype building of tangible items, so forgive me if this is a stupid question, but is there a reason you are making this out of metal from the start and not something easier to work with to determine the size, look & feel, etc? I would think it would be easier to build a template out of wood or some other composite material.
Nearly all my R&D projects start with 16ga steel as it is quick to cut/drill/bend/form into the needed shape. Once the template is done, it is easy to take precise (+/-0.005") measurements from the part and draw the part in AutoCAD. Before I send the drawing to the machine shop for reproduction, I make a prototype from the drawing dimensions to validate their accuracy. Once I verify those, I send the drawing to the machine shop to reproduce. Once I am done with the 16ga template, I toss them on a shelf in case I need them later.
Wood isn't dimensionally stable over time, especially with changing humidity levels in a non-climate controlled garage, so getting the same level of precision would be very difficult if not impossible. There is also reduced ability to tap holes within wood as well. Plastic or composite could be an option, but metal fab and machining is my hobby, and I enjoy working with metal.
I didn't show them, but I made about 5 iterations of the 16ga templates to fine tune the 2D placement of the components. I switched to aluminum to dial in the precise 3D dimensions and create the 3D template/prototype for test fitting as well as to validate the ability to machine the part.
So in short, there normally is a method to my madness... I wouldn't say it is the best, but it works for me.
I continue to refine the oil pressure sending housing. I flipped the location of the stock LS4 oil sender and the spare 1/4 NPT (the new one is on the left). I have one more tweak to make to the drawing and I will send it off to be quoted.
Since I am still bogged down with a few details on the custom CNC water pump and accessory bracket, I decided to work on a more simplified (relatively speaking) water manifold/thermostat housing to be used with an electric water pump. This should be speed up progress, create some other potential applications, and let me get a feel for CNC costs for this setup and the potential costs for the mechanical pump setup.