Dave - you're in a position that very few of us are. You actually work on race cars and know all about the products and technology and your excellent model detail reflects that. I will probably never see a Mark Williams 11" rear end in person, but I know from what's available to us, the TDR reproduction is a thing of beauty.
This is a photo of a 1/8 scale TDR rear end with the disc brake and hard mount options.
Their turbo chargers show the turbine veins, bolt holes are provided in heads, header flanges, pulleys and many other parts, their 4bbl Holly is a thing of beauty for 1/16 scale. There are many quality resin products available, but most don't have nearly the detail of TDR items. Are any of these products (especially from the kit manufacturers) true to life? I doubt it. But can I tell the difference? I just want as much detail in the parts I can get to make it look realistic to me. TDR and a few resin guys do it.