Looks great glad to see you back on it. Is that Saito next to itr what you are going to power it with?
If you use an OS and mount it sideways you will have to modify the front top cowling to allow for the motor to extend out of the side of the plane. I mounted the RCV at a 45 degree angle so I could get both the carb. and the exhaust inside the cowling of the front of the plane. see photos of build log. With a standard L shaped motor the inverted mounting location of the motor is the only arrangement that you will be able to get the motor completely inside the plane.
I'm going to put in a remote glow plug and run a glow igniter to forestall the problems you mention. I just think it is a shame to mess up the nose of a P-40 with the head of an engine sticking through the side of it.Fully aware and know what to expect. Dad built the P-51 and FW-190D kits while I was still in grade school. Not worried about a hidden engine install. Historically inverts engines flooded and didn't run as well, not to mention the difficulty of attaching the igniter to the glow plug.