I'm sure that there is a classic 158 grain load for Bullseye, but I'm not familiar with it. However, my go-to load for the 158 grain semiwadcutter in .38 special is 4.3 grains of Unique. It's been my standard load for about 20 years and shoots very, very well in every revolver I've tried to use it in.
However, the standard .38 special target load is a good full 148 grainwadcutter and 2.7 grains of Bullseye. Lots of folks have used that over the years. Are you sure that the rules specify a 158 grain bullet?