Not exactly sure what youre looking for but, sheesh! What you have explained sounds gnarly. These trans are damn near indestructible. Sounds like a PO has gone and fubar'd some stuff on you. Send us some pics of the damage so we can get a better understanding of exactly how bad your dilema is. Meanwhile, I found this on ehay:
http://m.ebay.com/itm/Black-Painted-...257Ciid%253A18
Also, I did a search for sm420 (we have determined you are sm420 for sure?) all over Craigslist for the old cast 420. Nothing really going on nationwide. I did it for sm465 and it revealed many potentials around you within half a days driving distance. Maybe someone can chime in on me and tell us if the sm465 is a direct replacement for the 420 or do you need to adjust or cut things like driveshafts or the such. Good luck.