Need Help

[OneBad71]

Hello, I have a 71 C10 that started as a project in 2006 when I took it apart. Life happened and I started back on it last year. It was a small block , auto truck. I installed a Big block 496 with a TH400. It is a roller now and I'm working on getting the truck pieces painted. When I ordered the motor from Blueprint I ordered the Long water pump kit for it. I installed all of the front group and I decided to mock up the core support. What i;m seeing is there isn't much room for a radiator with electric fans ? Was I supposed to go with the Short water pump set up ? I am so bummed that I really don't know what to do ? I'm 68 and i'm not a mechanic but I can work on cars to a limit.
Any help on what I need to do , or if you have been in my position would be Greatly appreciated ! Thank you, Dan