i might get a 255 inline fual pump instead of a 255 intank pump. it of course will still have the factory intank pump. will it flow as much as an intank 255 lph fuel pump? will it flow more? anyone have this?

 

Why? All you're doing is raising the fuel pressure slightly but will still be limited by what the factory in-tank pump flows.

I remember some of the Z28 guys would do this on blown/nitrous applications to relieve some of the stress and "help" the in-tank pump (Mostly because the in-tank pump was a PITA to reach).

Go with the in-tank for the Evo. It's easy to replace and cheap.