Ruger will not sell their action, you have to buy the rifle. That being said.,The Volquartsen 2000 trigger group is hard to beat. I've not found any appreciable difference between an 18" barrel vs 20". I personally have a .920 heavy barrel that is 18" long. A 22LR has absolutely no need for a flash hider. What flash!? The aftermarket heavy barrels are more accurate than the stock 10/22 barrels. As per stocks,the Tacticool stocks are mostly designed for the factory barrels.
My humble suggestion...go to as many pawn shops as you can find and look for a used 10/22 to use as the basis for your project gun. Look at www.midwayusa.com
for aftermarket parts and price them out. Meanwhile, shoot the daylights out of your beater 10/22 so you know what the rifle is truly capable of. I'm a huge 10/22 fanand have built mine into a tackdriver. Beware, they can become a money pit, but are fun, all the way. FWIW, the match grade barrels are built to tight standards, and most won't feed CCI Stingers because that round is a bit longer than a standard 22lr round. CCI Blazer 22LR ammo is cheap and pretty accurate. I use Federal Gold Medal Target for accuracy work= 3/8" to 5/8" at 50 yards.