Get a spray bottle of Easy Off oven cleaner and a dirty old bath mat. Run hot water over the metal to warm it and spray the Easy Off all over, filling the barrel well. Wait 20 minutes. Put on rubber gloves and eye protection. With old toothbrushes, maybe a bottle brush, and some ###X steel wool, give the whole rifle a good rub down then wash off in very hot water. Scrub out the barrel with the Easy Off still in it. I guarantee you purple goop will come out. Run lots of hot water through the barrel. Blow off the moisture with compressed air if you have it. Otherwise wipe down and dry on a woodstove or with a propane torch, just until the moisture evaporates. Be careful not to overheat thin parts, if they change colour you've screwed up. Spray down with G96 or whatever and let sit for a few hours. Wipe down and you will be amazed how much better it looks.
The stock is best left alone IMHO. Whatever you do, don't Easy Off it. Old stocks are like fine old furniture and when you strip them you ruin them and their value.
Live with the cracks is my advice or get a really skilled stock or furniture repair man to do it for you. There are some really gifted amateurs around too.