That's true. But Model Chrome is not telling you that on their Facebook .I was just bring up that you have to provide them with a perfect part. They will not do the work for you. I know if you send me a bad part. I will send it back unfinished.
This is really not a new process. It’s the same process they use to silver plate mirrors. Centuries old. I just bought a kit. And will soon start doing platting. This is a chemical process not real chrome platting. Thickness depends on how much you apply. About the same thickness as vacuum platting. But what they don’t tell you is that your parts have to be perfectly smooth. Any flaws in the surface will show up. They like me will not finish the parts for you. So I would recommend that you paint a black or very dark blue base coat on your parts. This way you will see the surface shine that you will get back. If it is shinny and no marks. The silver will coat it and shine like chrome. The clear coat is sprayed on it to protect it. An automotive clear urethane is UV protected. It will not turn yellow in time. I don’t know about Model Chrome. But they will tell you that they are not responsible for under surface finish. What you see is what you get.
I never have problems with bubbles. I always pressure cast. I mostly do two part molds. Some cheaper resins have a tendency to naturally produce bubbles. Careful, Some resins will foam up when you vacuum. I use Smooth-On products for all my casting needs.
I use automotive quality greass and wax remover. 3M is a good brand. But Turtle Wax sells a bug and tar remover at the parts store. Same thing. Removes all wax and sillicon. Just wipe it downd with a well soaked rag. Do this before any sanding is done to you parts. Use it again before you paint. Removes oily finger prints.
I use Smooth On too. The way I make my molds is differt from what others use here. When I pour my molds. its a closed mold. Meanning I pour resin into the mold threw funnels. In the mold has runners and gates. Any area that I see that will trap air. Such as the rim of your wheel. I cut a vent into the mold to have somewere for the air to go out of the mold. I use a peice of .072 stainless steal tubing to punch a small hole into the top half of the mold. It has to bee tubbing. As it goes into the mold. It will cut a small core out of the rubber. I push it all the way threw to the top of the mold. This way the air and resin will flow freely into the mold. Eventhough I use Smooth On 310. It is a no air bubble resin. I still use a pressure pot for curing. no more than 35 psi is need to collaps and bubbles trapped in the mold. Useing this method. I never have any air bubbles.
Most early SBC are all the same in outward apperance. Only differences are valve covers and air cleaners. There are many resin castes that sell only the valve coers and air cleaners. The valve covers in the picture you posted are early vett covers. Air cleaner early BB maybe 66 - 68. Kit bash for the engin and find a caster that has the valve covers and air cleaner you need.