I just re-finished a marlin 39 stock and 3 sets of Hogue grips. I don't like the wax finish Hogue puts on they're grips. And the Bisley's needed a little fitting.
I used a teak oil finish. They came out looking good. I all so used the teak oil on a set of walnut BuckMark grips I just got. I think they came with no finish on them at all.
I've used the true oil in the past with good results too.
It isn't hard to do yourself. Those Ruger grips would just need sanded and then decide if you want to use a stain or not. If it was me I wouldn't.
Then apply what ever oil finish you want to use.
I would recommend at least 4 or 5 coats of oil, sanding with 00 steel wool in between each coat after they soak in.