Depends if the stock is soaked in it. A stock that's full of cosmoline will continue to "weep" long after a cleaning unless you cook it out. Everything else is no problem to clean, though.
I was doing enough of them once upon a time that I made a little cooker out of some plywood, insulation wrap, and some light bulbs.
That is correct, heat is the only way to get cosmo out of the stock.
Chemicals are for the metal parts only. With the heat method, there is much much less taking it apart. I have seen more then a few folks do the car dash trash bag trick, wipe it down, oil it up and start shooting Mosins. The SKS I would want to check over a little more though.