Since the 737 is supposed to replace the 727 on domestic routes, not add more routes; my guess is that it won't result in a very big bid for hiring.
The majority of +60 guys go to the back seat of the DC-10. I don't have any numbers for you on how long they stay there (kids graduate college, alimony runs out, ect.)
A large part of the equation will be how fast the 737's arrive, and how long the training course is.
However, we are going to see a very large number of retirements over the next few years, with alot of growth in the widebody jets. That is where the money is - international freight since the domestic side is basically flat.