A couple things
The -4 is a bit of a challenge due to size and various configurations. Certain things must be in proper orientation. First concern is engine control cable routing and pass throughs. For my carbureted O-320, they come out through the tunnel low and near centerline. Cabin heat, depending on your plan for that has to be routed with ducting from the heat muff. Your oil cooler location can also impact what can be behind it. Here are a couple pics of mine, though not prefect, have worked well so far. My battery is in the tunnel, but I have room to go on right side of firewall if I want. My heat box is on L/H side, but muff is on R/H pipes, so SCAT tube runs around back. My pressure sender manifold is on L/H upper side. The brake reservoir needs to stay centerline and high. Fuel line and smoke system lines are in tunnel down low. Both solenoids are in tunnel on cabin side and out of the way. Really need engine hung to know some things or face relocating them later. Plan carefully, cut/drill once!
8A7 / Advance NC