Hyd. roller lifters in a non-roller block?
To your side question: I have performed several head gasket jobs on various engines over the years. If you are real good, you can have the heads off while the engine is still hot. What happens is during the dis-assembly process, one of the first things to happen is taking rocker arms off and then pushrods out. If the engine is still hot, the lifters may stay pumped up due to residual oil pressure so to speak. When you go back together, the lifter is "up" and when you set the rockers on (side note: this happens more often on pedestal mount rockers where there is no lash/pre-load adjustment, just a torque spec for the rocker arm bolt) the lifter does not bleed down, it just opens the valve instead. Even rolling the engine over will not collapse the lifter initially. It usually has to set for a while against spring pressure to eventually bleed down and close the valve and allow the engine to start.