You've got a Schlage H Series. They still make and manufacturer them. The top hole for the deadbolt should be bored to 1 1/2" hole, bottom to the standard 2 1/8". Both of which are still standard to the H series so you can buy one brand new it'd install just as well as a new one in 1987 would have.
You can also elect to replace it with just a deadbolt and lever/knobset, although doing so will remove the functionality of the H series lockset. It appears you have an entrance, single locking function which is:
Entrance Single Locking - Deadbolt thrown or retracted by key in upper lock from outside or by inside turn unit. Latchbolt retracted by either knob (lever in your case). Turning inside knob retracts deadbolt and latchbolt simultaneously for immediate exit.
A lot of information found in
Schlage's Website. Very similar to the G series (now discontinued but still being sold), so make sure you don't confuse the two if you do decide to replace it with the H series.
