Good work. I've done this as well. The graph for my Saunders 4500 looks very similar to yours.
I've also made a graph by using a cheapo color enlarging meter (I bought a Minolta PM2L) and simply measured the filters I have from Ilford and then adjusted the dials on the enlarger to give the same readings. Easy to do, no test prints required, no real math involved, and those color meters are cheap these days.