Cummins and others used to sell a machine to do this, it pumped the old oil out, filtered it and pumped fuel also to mix the two thouroly before pumping back into the tanks, about 6 gal to 300.
The old dark fuel we used to get in Mexico had more power than ours, and #2 has more power than #1 so I see no problem but 60% is a bit much, thats almost bunker fuel, and starting a 17 deg.?