On a Kibler kit I would raise the grain with every sanding grit. But remember to be correct it should not be over finished.
in fact I would simply sand or scrape away any modern machine marks then carefully sand with 220-320 grit for a final. SMRs are not supposed to be finely finished or highly polished. For surfaces like the lock surround I would use a hard, flat sanding block and lightly used 400 grit since the lock is already close to the final wood surface. So “lightly” is the by-word here. Just enough to flatten and whiskers.
I never sand with paper coarser than 120 and then use a lot of care.
Now on a brass mounted Kentucky with carving and such I sand to at least 400. It makes getting a nice finish on the stock easier. But I am not a built up finish guy so,,,,
Also. If you have (or make) a SMOOTH burnisher, it can be hard wood, antler or a steel burnisher, it is possible to burnish the first coat of finish when its still wet to rub down and then the finish “glue” will the whiskers in place. Especially if they were raised by the Ferric Nitrate stain. But on curly wood be sure to angle the burnisher across the curl to prevent/reduce rippling and do not use excessive pressure. Also burnishing will not cure tool marks or rough sanding, the process may smooth it somewhat but its still going to show. But on a SMR this is not critical. I would probably raise the grain on a Kibler before any wood removal/sanding operation. And I would leave the buttplate in place for sure and maybe the trigger guard depending on how much wood needs to be sanded to smooth the toe line.