[SSSammy]

We have a local club member with a JBL and I have wrenched with him, so I know you have to pull the motor to get the tranny and bell housing apart.

Changing to a 3/4" master is easy. Tilton makes one with the same bolt holes as the 5/8". You should do that, it does not require taking anything else apart. Even so, you will probably need to adjust the throwout bearing clearance. The concentric slave is on a threaded collar. You can possibly rotate it by hand to close the gap to the diaphram. You have to undo the hydraulic lines first, then poke them back into the bell housing. If this is the case then:

Use a long screwdriver or other lever and collapse the bearing piston as far as it will go.

Reach your hand into the fork hole in the bell housing and rotate the slave cylinder on the threaded collar to the left (lefty loosey, righty tighty) until it closes the gap to about .1-.2"

Pull the hydraulic lines out, making sure the bleeder is on top. Reconnect, bleed, go play ..

Sam