Can you turn an automatic 1990 Nissan 300zx into a manual transmission?

Yes, you can convert a 1990 Nissan 300ZX from an automatic to a manual transmission. This process involves several steps, including sourcing a compatible manual transmission, clutch components, a manual transmission crossmember, and modifying or replacing the driveshaft. Additionally, you'll need to address wiring and possibly the ECU to accommodate the manual setup. It's a complex project that requires mechanical skill and knowledge of the vehicle's systems.