Beautiful work. I think there is a secret to making a model of such complexity... it's pretty simple, guys like this have enormous patience.
Multi-cylinder IC engine models have an enormous number of identical parts, especially fiddly little things like valve C-clips, valves, rockers, etc. If you look at the huge parts layout before final assembly, there's not one part that isn't within the reach of most of us here. If you have the patience to machine 36 valves from stainless steel, 18 pistons, 36 rocker arms, then after a LONG period of time, you will have a "no-machining kit of parts." Assuming you worked to print & tolerances.
If you look to each part, each sub-assembly, as a mini-project all by itself, it helps. You machine a head, finish it, admire it, consider it complete, and you get that rush of satisfaction. The part gets carefully wrapped, labeled, put aside, and you move on to the next.
What is definitely on another plane here is the design aspects. Very few men have the skills to design something like this. The maker also has outstanding hand finishing skills. He knows how to file, how to use abrasives, and this takes a nice model and raises it to another plane in fit & finish.
Hopefully, something like this is inspiring rather than frightening. I know it inspires me.