Cary Lamari

Hi, I am new to the world of LS1. I am building a 69 Chevelle and thought it would be cool to install a LS1 in it with a 4l60E. So I bought a 1998 LS1 from a guy. the guy lied to me about it but I heard it run so I think I am ok. he said it was a 2005 as it was in his 05 corvette but it isn't it is a 1998. He was a real jerk. I need some help though. The previous owner took a lot of parts off the motor and I am trying to piece it back together he also butchered the steam crossover cutting the center section out and put a rubber hose in between the front pipes and also in between the rear pipes. I picked up a 4 port crossover from a 5.3 it looks the same except the front radiator tube sticks up. My problem is now I can't seem to be able to reinstall the original intake manifold. It is a 98 intake with two fuel lines one supply and one return. Is there something I am doing wrong to get the intake to go down or is it the crossover is different on the 5.3. I would really appreciate the help. It took me forever figuring out how to install the motor in the Chevelle but that is done and I am buttoning it up now. Hope to start it soon