The Borgeson box operates at a higher relief pressure than the OE Saginaw box. We sell a pump with a 1350 psi relief and the proper flow rate for the box. Removing the shims from your pump isn't enough to get the job done.
Curious, I have the OE saginaw bought new a few years ago but changed the flow control valve to this:http://www.jegs.com/i/JEGS-Performance-Products/555/60791/10002/-1
what makes your box different? I do have to put in some extra arm effort during autocross would your pump eliminate this being better matched? (I should mention I'm also running with fast ratio pitman/idler arms)