for gettin' the cartridge bearings out, the secret is persistence.
short, sharp taps with a small hammer on a block of wood against the axle.
gettin' the new ones in was no problem. for the cassette side, you can use
your DIY headset press, using the old cartridge to protect the new one.
for the opposite, stack both old cartridges atop the new one, followed by a
large flat washer, then a small piece of wood. tap gently until the washer is
nearly flush with the end of the axle. then add a spacer and continue until
flush, and axle doesn't wriggle side-to-side.