Here is a recipe for wood based substrate for edibles/medicinals that has worked well for me .I'm sure it could be tweaked, but it's a winner and it works great just the way it is. I dont use Vermiculite and I dont use wood chips .( though I just picked up a huge bagged mixture of chips and sawdust to play with)
Just wood pellets,Gypsum,and Wheat Bran.I've got photos but dont have the will right now to dig them up.I'll work on that later.
These ratios will make 13 lbs. of substrate which will provide enough sub for 2 - 5 lb. blocks and 1- 3 lb. block (with a little left to toss to