http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33615&item=2451498216
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33615&item=2451282936
Here are a couple on ebay that might be worthwhile. If I were going to build mine back I believe I would want to go with new pistons. I have toyed with the idea of cleaning up the pistons I have and putting it back together with new sleeves/rings, etc. I will eventually get around to it.
One of the local independents has just recently rebuilt a 5 cylinder turbo engine that may be available. I did not ask him why he was rebuilding it. If you want his name/contact number let me know. He has been in the MB business for 30+ years and does good work.