I'll describe my method, for what it's worth. I don't mask off the checkering. Since it's going to be re-cut anyway I just sand right up to it and if I go too far, so what? Re-cut the checkering when the finishing is done, and seal the checkering with a mix of the varnish you use and some oil to thin it, work in with a toothbrush, blot away with lint-free cloth. Or, just use whatever oil you use on the stock and blot it dry.
There are those who advocate filling the pores with sanding slurry achieved through wet sanding with the finishing oil. While that works, it's not the best- is not prone to staying put and is prone to shrinkage over time. Even if one is hell-bent on using an oil finish, the best way to fill pores is with varnish or epoxy. Slather it on, sand it off down to the wood surface, repeat until all the pores are filled evenly. Proceed with whatever finish you're using. Since I would use a barrier finish for the stock, I just start right in with it. The sanding between coats will cause the pores to slowly fill more with each successive coat. Keep going for a couple more coats after the pores are level full, then rub it out to give it a soft sheen not unlike an "oil" finish.
That was a lesson I learned the hard way many lifetimes ago. I filled the pores on a Winchester 94 stock with some kind of "pore filler" off the shelf of the hardware store, then finished with oil. I got caught in a monsoon and sat there watching the rain slough the finish right out of the pores. Another time I used the "sanding-in" method of pore filling. A year later I was re-doing the stock because the stuff shrank into the pores making it look like I hadn't done a thing. The crazy thing was I was convinced I did something wrong, not that the method was suspect, so I repeatedly used that method a couple more times. (What's the definition of insanity?- Doing the same thing over and over and expecting different results.) That's when I knuckled down and set out to learn the right way to do it.
Like most things in life, the quality of the end product is a reflection on you, and how determined you are to do it right- no matter how much time/labor it takes. Unfortunately there aren't many quick-and-dirty panaceas in this game.
