1998 Chevy Silverado Won't Start

I have a 1993 chevy silverado and burnt up the v6 engine that it originally had. I put a vortec 5.7 liter v8 in its place and swapped out the dashes. I got the engine out of a 1998 z71 that had been wrecked but still ran fine. The owner had taken very good care of it and I actually drove it around the house. Everything worked fine. The fuel pump works and so does the starter as well as the rest of the parts to my knowledge. Obviosly something isn't working properly or it would be running properly. It turns over but will not start. Like I said everything worked before I took it out of the original z71. My 1993 is two wheel drive if that helps