@manilx
It is not cheaper, but it draws about half the power when idle. When doing work the power still gets up there, they are 60-90 watt computers, which is still less than the 300 watt capable HP servers at full go.
If you really stress your lab a lot, real servers are a win as they will draw less power for more performance, but if yours is like mine and it idles a lot, cutting the power is nice. I'm about 200 watts at idle with the above, and that's two labs worth. I was 400 with the single old lab system.
Mounts are cheap book ends, drilled and screwed to that specific shelf, and drilled for short m4 thumbscrews to get into the VESA mount on the t740.
If anyone reading this wants to duplicate, and they see HP T755 cheap enough, I recommend these because it has 6 cores / 12 threads over the t740 with 4 cores / 8 threads. Both are DDR4 sodimm and top out at 64GB. Both have a PCI 3.0 x8 (x16 slot) that takes half height cards. And if the BIOS is locked, you can write over them with a programmer and enter the data needed to function (see badcaps forum for my guide).