Nope - the only instructions are the PDF from 1990-ish.
Have you removed the Floppy Drive? That's gotta go, too, in order to remove the motherboard.
Once you have the motherboard removed entirely from the case, I can't recommend more highly that you get these 3D printed
. It's almost impossible to mount the Rejuvenator on top of the golden pins without a guide of some sort. You'll print those then push them onto the tops of the pins and only push them down about .5 mm. You want the gold sticking out, but not too much. Then once all the holes are aligned (you should try to triple-check your alignment) you'll firmly push down on the Rejuve to get that thing to go down. And the guides will slide down the pins as you go. It's a PITA and the hardest part about the installation.
Also, as you push it down and get near the bottom, you'll very likely need to double-check the blue capacitors are going through the rectangular cut out. The tolerance is nil. Honestly, that's one part of the Rejuve I I wish could be redesigned so that gap wasn't so tight. Finally, make sure you don't bottom-out the bottom of the Rejuve onto the top of any of your components down below. The new design will ride really low, though, so don't worry that it seems to go all the way to the floor.
Do you have the 1MB of RAM to go onto your Rejuve's board? Those can be a bit challenging to locate these days.