Its been about fifteen years since I was down there, but Johns Salvage in Cabool, Missouri, hwy 60 & 63 back then had rows of the old Mercs lined up side by side. Many were complete cars with whole engines from the pan to the top of the oil bath air cleaner. Phone (417) 962-3237 and ask if he still has some. Warning, don't fall out of your chair when he tells you what he wants for his parts.
There's another John's Salvage located in Seguin, TX you might try. He specializes in FOMOCO products and has stuff going back to the '30s at least. He has a website but you'll have to call or email him to see if he has a particular part. Very reasonable prices.
Tom: I am very interested in contacting you. I tried via another site sending you a private mail. Please drop me a line at vmilkeg at paniplus dot com dot mx