Electric vacuum pump vs. EVAC
I have used the pan evac system with a 3" exhaust and Flow Masters before and it worked. But, I didn't use the kit valves as the suction needed for them to open was too high. I used aspirator valves from a /6 Volare air pump setup. I don't remember what year or what the part numbers were though. I'm not even sure if they are still available. Additionally I cut pie shaped cuts in the tubes welded into the collectors facing the exhaust flow. This increased the suction to open the valves.
I have seen the vacuum pump assembly make as much as 30 horsepower over an evac system on the dyno with a 351 Ford Super Stock engine though. So depending on what your application is you may want to consider that money well spent.