I own a 1979 Dodge pickup with a slant six.Only driven about 500 miles per year(MAY to Nov.) Current fill is 5qts.5w-30 TropArtic,16ozs.SLOB,and 16ozs.MMO.Truck not using any oil.I have 2 gals. of Mobil Delvac 15w-40 CI-4plus/SM that I'd like to mix 50/50 with a 5w-20 or 5w-30 to use it up. Should I use Mobil Clean 5000,TropArtic blend, Castrol or Valv.conventional,or are they all miscible? Any adverse add pack reactions?THANKS.