Of course, it would be 8X57JRS, but if you have dies for the rimless 8X57 they work fine.

If you cannot get load info from the manufacturer, load up four of each (with the bullet weight you desire) in incremental loads from the low end up and see how they group. Then fine tune the charge from the best load.

I bet some guys here have some 8mm pet loads they could pass on to you.
I am still working up a proper load for my 8mm double so I am not much help here.