Tom; I've been cruising the net and think I've answered my own question. The last 3 letters on the dist pad is the application code. In 1970 they changed this code from a 2 digit number to a 3 digit number. Therefore my engine must be newer than 1968 and therefore it must be a 1978. They didn't make a 250 in'88 did they?
I got the info from this web site;
http://www.camaros.org/drivetrain.shtml

thanks, Al