It may be wiser to just swap in a t5 t56 or easier yet a GM auto. I'm no Z expert, but have never heard of an adapter kit commonly used for the 280 5spd. Even if there is one I dont think it would last behind your V8 for very long. Do you know of JTR conversions already? If not here is the link.
http://www.customconversion.com/Pages/Datsun_Z_V-8.html