fairly soon I will be at the stage where I'll have to make a decision on this myself.
The engineer in me says the mast should not touch the block or tabernacle rear face. The book calls the halyard to be "guitar string tight" meaning the shrouds will also be tight, and they are designed to carry all of the aerodynamic loads. If the mast bottom touches anything, it will only add a bending load twisting the tabernacle forward without adding any strength. And any stretching or movement of the shrouds will only add to this bending force.
My vote is to use the shroud length to set the mast rake, and maybe only use the block to calibrate the angle.
Pasi