In this world file are 3 nearly identical spruce farms, 2 of which work fine in 1.12.x and the one on the far left hand side when viewed from the blast chamber. That one works in 1.12.x, as well as 1.13 for several snapshots, most pre releases, and the 1.13 as well as the snapshot just after that release. Snapshots are buggy, so you cant really expect anything, but 1.12 is stable enough to load the device and enjoy some of its mechanics, which are interesting and show many different styles coming together in perfect harmony. Harvest time is right about 20gt, maybe a bit under, who knows, that means that if it takes you one full second to place and grow a tree, then you have a rate of 30 trees per minute. The biggest bottle neck is placement time, to be honest. In the main body of the devices, I'm not exploiting any bug like behavior, however in the far right hand side model, right before the couple of disassembled body pieces, there is a model which uses a tnt duper. As for the body pieces, those have been laid out to make it easier to see how the machine is being powered. Most of its mechanisms will work all the way back to 1.8 if properly wired.