Well some argue that the heads can be welded. But its a temp fix at best. The 14 heads were the ones that cracked. Anything 17 and newer is fine. The 350's had the 17's, so if you find a junk one of them you can use the head. 22 is the latest.
The bottom ends are very tough, mine has 254k and burns zero oil, and will pull the car to 60 faster then MB claims it should. I wouldn't even touch the bottom end if you got the head off and the cylinders looked good. Not worth it. Replace the timing chain, rails, tensioners, deal with the head, time it and your good for another 200k+.
If you want to do the bottom end, do a search into the archives. Also get a service CD from MBUSA
MB Tech Manuals from MBUSA cost $19.99 plus S&H
http://www.peachparts.com/shopforum/showthread.php?t=142445
You can probably get away with new liners, rings, and bearings. Also don't forget the oil pump and its chain. Really at 220k everything should be in pretty good shape.