Could i drop a small v6 in my....

Could i replace my 1988 nissan pulsar NX's little 4 cylinder with a small block v6?

Anything is possible if you are up to custom making enough fitment parts. You could get a VQ or VG engine and drop it in. A 3.5 VQ engine from a new 350Z might be harder due to the age difference but it would make for quite a ride. A VG30 from a Twin Turbo 300ZX would be a bit on the heavy side for your car but it will make 400hp with simple exhaust and intake upgrades. 500 hp at the wheels is pretty easy with this motor and might be something to consider as it may be heavy but it's fairly compact and the age is about the same as your pulsar. But to my knowledge, nothing will drop straight in to replace your stock engine.