The side hole lets the oil in, and the top hole lets some oil and any air out. The pushrod regulates how much oil gets out, but it is lubed by the oil running down it from the head. Those lifters are similar to more modern designs and should work better if the oil pump sucks air.
I think the side slot is a bad idea, since you could starve the cam bearings and top end for oil by doing that.
Last edited by 4ontheFloor; 02/12/2008 9:12 AM.
