Smoothing/Mirroring Firewall ?

[Billhilly]

Hey Guys,
Working on my firewall and want to plug the 'blower hole' on the firewall and 'mirror' left hand side contour, over to right hand side (kind of like the red line below). Is this panel normally just 'cosmetic', I mean looks good from the front, but has a gap between firewall/cowl area?? Or do you some how weld in a 'bridging' piece to extend the channel where the stock wiring harness runs? (Want it to look like the bottom photo).
Any thoughts on this appreciated.