Basically, from everything I know about them, The Stevens 200 is pretty much a no frills, no accu-trigger version of the Savage 110. the aftermarket parts should for the most part, drop right in with maybe minor fitting in the stock. I hanv't worked on a moden savage or stevens (most of my work is on shotguns) but I would say it can't be that much worse that working on anything else. Just use good punches and good screwdrivers that fit the screws snug and properly. otherwise you'll bugger them up good. Work carefully and you should be OK. I'd leave the barrel work with somebody with a lathe and the correct headspace guides. you might also want to look at the hart barrel, too. They are pretty good.
good luck!
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