Quick case of brain fade. Neighbor is building his first plane, and asked about left/right engine offset. If mempry serves, left offset (as seen from behind the plane) is preferable to offset p-factor. Is that right?

Standing behind the rudder and looking towards the engine, a lot of planes will trim out better with the engine pointing slightly to the right. Some also benefit from a small amount of down-thrust. Check the plans to see if it's needed and for the specific amount, but usually it's between 1 - 3 degrees.

If you're unsure it may be best to mount the engine straight to see how it flies, and then adjust by putting thin washers behind the engine mount as needed to add right and/or down-thrust.

EG

1/2A engines with 6 inch props don't have a lot of gyroscopic torque working against the average sized airframe.......so you can be off a little with how the engine is aimed and the effects won't be that great. You can see left / right issues when you are doing an extended verticle line at a moderate speed, or while in a true hover.
Up / down thrust is used when the thrust is either well above or below the wing, in this case the thrust will try to get the plane to loop if there isn't a corrective thrust angle built in. Typically a high wing plane with a low mounted engine might need some down thrust. I have flown for many years and have had as much fun as anyone else without using special engine thrust angles, except in extreme cases where the design layout demanded it, or when I used to fly models with 16 inch props....then the effects are bad if the angles aren't correct.

Thanks, guys. It's amazing but I think that I may have hit the age when I've forgotten more than I know!

Hmmm! At that age sometimes p-factor means how far away is the "Porta Potty". [8D]

George