The books is no longer relevant as it references the sierra as the donor, so it's no longer a VIABLE build. That means there is little new interest. ( The sierra forum itself is very quiet as the ENTHUSIASTS have been priced out of the market, same on the XROC forum. )
It's also much more difficult to build now, not only has the donor become expensive, but nobody builds Chassis, Chassi Kits, Etc.. Body work is difficult to source.
So the stream of new builders is so much slower.