RE: EF 4 speed to 5 speed swap?
you have 3 options
for one it will have to be out of a 89-91 civic Sedan/hatch/crx
you can get an SI trans, DX, or HF
Si is the most agressive
DX is just like the si except for 5th gear
HF is geared for gas millage...aka slow
bolts right up..you said you had a 90..as long as you stay away from the 88, you won't have to replace your clutch/flywheel setup but it might not be a bad idea to replace it up
The 88 transmission has different clutch setup but will bolt up..just requires you to get new stuff.
DOHC ZC EF