Yeah what Freestylers says is true,you need to groove or else your cam wont live long.
I forgot tho tell you that,the early carby engines had that groove in them,the later injection engines had a bit of modified oil system without that groove,where did you get that cam from?
From a early or a late 2500?
The later 2500E had a diffent cam than the earlyer ones for more torque in the lower rpm area,s.
Just let a groove machined in that 2500E and it shut be okay.