IMO its like most everything mechanical, if you have the time, dedication, and patience most anyone that can turn a wrench can do it. Its not as if you are going to be doing the actual machine work (unless you have that ability) but just the assembly. With a bit of reading on these sites and a few conversations with guys like Jason, Dave, etc
Between here and PSN there is such a wealth of info its amazing if you take the time to look for it. These guys over the years have dropped very good tidbits of info on how to get the most out of these engines when you build them. That along with also very practical and what might seem common sense to a experienced builder but would be missed by a a first timer. Such as the correct orientation for connecting rods front the rear.
I plan to build my next engine myself. It will be the first diesel I have ever done by myself.