They did come with a 5-50 fill, but its not necessary to run. These coyote motors can run any weight from 20 to 50 and in between. If the car were going to be used at HPDE events regularly, then I would stick to heavier weight, otherwise a 30 weight is just fine.
Op is a buddy and I have seen this car person quite a bit, it looks great and has been meticulously maintained. Good luck with the sale brother!