340 block with NO main caps

No need to bury them. The temperature change is what "seasons" the metal. The bigger the extremes the better. Faster to do in a heat treat oven and cryro chamber. Common practice for straight edges, parallels, and other precision machine alignment tools made from cast iron. There are all kinds of stresses built up in a casting and temp change can cause crap to move, a lot more than you would think. For 98% of applications, the tolerance stack up compensates for the variance.