shimming hydraulic roller lifters solid

I have done it a few times with FT lifters. Roller lifters would be no different.
I used s/s washers stacked up to form the spacer under the piston. There is a small shoulder on the bottom of the piston that is used to hold the valving mechanism. Best to grind that off so that the bottom of the piston is flat, more surface area then to take the load.