The Hi-Zack first appeared in Zeta Gundam, the first in a long long line of Zaku upgrades, and a striking design (despite the fact that it's really just Gundam MK-II fodder). In the '80s I built the 1/100 scale Hi-Zack from the Zeta Gundam model series. It was a nice kit, as were most of the 1/100 models from that series, but had some flaws. The head is just plain awful, the articulation is poor, and those darn rubber power cables are ugly and unpaintable. After a ton of work, I've built the Hi-Zack I've always dreamed of, a mean looking, well articulated, Master Grade style Zaku worthy of the name Hi-Zack.
This model won first place in several Gunpla competitions, leaving me with prizes in the form of more kits I'll never get around too. The build is perhaps moot at this point, since Bandai released a MG version years ago, and many of the more complex joints I made are commonplace these days. But it's still a good read. :)
This model has been heavily reworked, I'd say it's about 30% scratchbuilt. Nearly all of the joints were rebuilt, power cables were replaced, most of the arms are scratchbuilt, a much needed facelift was given, and a lot of details were added. The build log is divided into sections, working our way down from the top.