Your muncie M21 is on ebay, I asked the seller for the vin and his response was 19N502272.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=200141895431&sspagename=ADME:X:RTQ:US:11 (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=200141895431&sspagename=ADME:X:RTQ:US:11)
His ad states a trans build date of Jan 1, 1969. Either the date or the VIN is incorrect.
I'm currently out of town, so cannot reference my manuals, whats the estimated fisher build date for that vin #?
http://www.camaros.org/geninfo.shtml#HowMany
Sept 68
E-mailed seller, I suspect it's actually 9N582272.