This transmission is listed and is stamped with 40887 but no prefix. Could be a possible '68 with build date of P 8 H 28 but it also has ct8 stamped on it. Could be a over the counter transmission in '68?
Here's the link '68 Muncie (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=161020549717&ssPageName=ADME:B:SS:US:1123)
Seller ID; fuelled_garage
Olive Branch, Mississippi
Yes, this was a service trans and that # is the "service replacement unit sequence number".
http://www.camaros.org/trans.shtml#service