If it's an SC300 W58 transmission you're using you can hook up the vehicle speed sensor directly. If it's an MKIII Supra W58 then you'll need a Marlin Crawler VSS adaptor.
An SC300 5-speed or MKIV Supra 5-speed ECU would help. Matching your OBD1 car for an OBD1 5-speed ECU is what you need.
You need a 5-speed shifter bezel, too. I'm sure there are other things. Not sure if the cluster needs modification.
Don't use the OEM Lexus/Toyota clutch even if you're not going with a turbo. Buy a simple aftermarket one.
I believe there is a definitive list of 5-speed swap parts in a thread on these forums.