New Engine preignites at 4500RPM

Shot it the dark here but maybe someone has a magic wrench. Brand new stroker build with Mallory electronic ignition. When the engine was being dynoed the builder was having preignition problems at 4500RPMs. When he bypassed the ballast resistor the problem went away and the engine pulled 560HP at 6000RPMs.
Here's my problem. I just installed the new engine with ballast resistor and it is preigniting at 4500RPM. It runs great until it revs 4500. This ballast resistor, distributor and coil were all working fine before we yanked the engine for build. Nothing has changed other than new engine. Any ideas? I know its a shot in the dark but just looking for piece of mind before my tuner tries to tackle the problem tomorrow.
Author: admin