David,
You sure have a couple of old-timers in there! (I noticed that the 10GB CX drive is a 5400 RPM drive, which is slower than the 7200 RPM 30GB LM drive, although both are Ultra ATA/66 drives and should work.)
The jumper block is the section on the connection end of the drive between the power cable connection pins and the ribbon cable connection pins. It has eight pins, arranged in two rows of four pins. The pins are connected vertically with the tiny jumper (shunt) to obtain a given setting. To set the pins, orient the connection end of the drive so that as you're facing it, the power cable connector is on the left side. Here are the settings:
Quantum Fireball Plus LM 30.0 GB 3.5 Series
Set it as Master: The jumper pin should be inserted vertically across the two pins in the jumper block which are furthest from the power cable connector pins. This is the DS setting, which may or may not be marked on the drive. Your drive likely is already set this way, but check to be sure.
Quantum Fireball CX 10.0 GB 3.5 Series
Set this one as Slave: The jumper pin should either be removed completely, or be inserted vertically across the second set of pins closest to the power cable connection pins, which is the PK position (park position) and is used to store the jumper when its use is not required.
You can easily remove a jumper with a set of tweezers or a paper clip with a small hook at the end, when it needs to be repositioned.
To pull the original drive, remove the entire drive carrier, which makes things easy to work with. Disconnect the cables to the drive. There is a single phillips screw which secures the front of the carrier to the base of the Mac. It's located at the front center of the carrier, just in front of the drive. Remove this screw and slide the carrier forward to disengage it from two flanges which secure it in the rear, then guide it up and out of the Mac.
Gary