I used to routinely mix 50/50 delvac 1 delvac 1300s in my 83 Mercedes turbodiesel (Ive sinced switched to 100% D1, but will probably go back to 50/50). Oil analysis results were good, and I never had any issues.
Some will say that you shoudlnt play chemist, and that there might be additive clash, even with two oils from the same manufacturer that share the same general name.
I dont think theres anything wrong, and I got an MPG increase equivalent to that or running 100% synth.
JMH