FIXED!

Here are my observations/notes:

1. used a handy, long-handled XTD-15XL Xcelite T-15 Torx screwdriver to get at the screws behind the top handle of the Plus case;



2. after sliding the Plus case apart, popped three cables off of the vertical power supply board, also popped off the floppy drive ribbon cable;



3. removed three phillips screws from the outside side of the power supply board, unscrewed the ground cable, and slid the board off of the chassis;



4. slid the mother board out;

5. removed five torx T-15 screws connecting the chassis to the front plastic Plus case and popped it out;



6. removed four phillips screws under the drive cage connecting to the chassis ;

7. removed four zinc phillips screws on the side of the drive cage connected to the drive itself and popped the drive out;



8. swapped out the old SONY MFD-51W-03 and in with the new one (interestingly, the old drive was also labeled a MP-F51W-03, while the new one, which came from a Mac SE was labeled a MP-F51W-23).



9. followed the reverse order to put the parts back together, and DONE!

Much thanks to fellow 68kmla'r Scott Baret for hooking me up with the replacement Sony MFD-51W-03!!!