I have a Ford C4 trans that I would like to install a shift kit in.It is probably from the late 60's or early 70's. How can I determine what year the trans is. I am told that there are two different kits for the trans depending on what year it is. On top of the case is stamped what appears to be CH573845. Other part numbers are also visible on the trans case and tail shaft. Any help would be appreciated.