I am building a 7, but they are similar. I have two Avery firewall pass throughs, one on each side quadrant. I am running all the sensor wires out the left side and will be using the right for power wiring. I have not completely decided about antenna, but it will likely be on the right. I will get some picts and post for you to see, and flyers to critique. (later on picts)
YMMV, but I mounted the engine to the mount frame then to the firewall to see if the locations would work. I have since removed it to complete other work before reinstallation. With a way to tilt he engine (maintain it level), install and removal of the engine/mount is pretty quick and easy, even solo.
One more thing, I found that the MAN P sensor fits nicely in the manifold on the left side, but will need a custom hose to reach the #3 cylinder intake port. I will be getting mine from TSFlightlines. Tom already send some fittings etc for measurements. Your distances will be different if you have a 320.