440 clearance to firewall

[phantom]

So, i'm currently working on the firewall, smoothing it out. Have factory A/C, i have welded all those holes up. Then i am planning to relocate the wiper motor, if i can find a way to do that.

Then i was thinking of maybe adding a second cover-plate outside the original firewall, so that i can hide harnesses and close the wiper hole, without welding it in.

How much clearance is there between the back of the engine to the original firewall?