In '88, the rear ratio is the same between manual and auto. I don't know if the ratio changed between '88 and '91.

The clutch hydraulics have nothing to do with the booster. You will, however, need the reservoir since it has a nipple for the clutch. You will need all the shifter components, console panel and boot. Make sure they get the clutch switch and wiring harness so that your cruise works correctly. Also the ENTIRE pedal assembly, clutch m/c and lines, driveshaft, speedo cable, front flex disk, motor mounts (yes they are different on the manual)

I am sure there are other parts that are more subtle. This is why I have always said that I personally would not do such a conversion unless I had both cars sitting side by side.

Also, your crankshaft may very well not have provision for a pilot bearing. Some measurement, good engineering and a trip to a general machine shop should take care of that part.

Best of luck. A manual transmission in these cars does a total transformation.

Enjoy,