I am building a twin engine plane and have decided after reading a lot of posts to put 5 degrees outthrust in the engines, they are 25 size. I want to keep the nacelles as compact as possible and so my question is can I mount a regular flanged engine with the nylon engine mount on top of the lugs and screw the mounting screws through the bottom of the engine and up into the mount. This will allow me to mount the engine mount closer to the center of the firewall and the prop to be mostly in line with the center of the nacelle. If any one needs a picture to understand what I am asking, I can draw one up.
Thanks, John

Just remember that the BOTTOM of the engine mount flanges are on the centerline of the crankshaft. So you would have to adjust the mount accordingly

my goal is to get the prop to the center of the nacelle. This would require me to mount the rear of the engine 5/16" to the side of the firewall. Will mounting the engine in the way described have negative effects on the mount. I understand that there will be more of a moment on the mounting arms since the thrust of the crankshaft will be a farther from the center of the mount.

There should be no problems with doing it

Not sure on all engines, but some makers go to the trouble of a secondary machining operation on the bottom side of the mounting lugs to insure that they are flat and parallel to avoid stress when the engine is bolted to a mount.

I'd keep that in mind when using the top of the lugs as a bearing surface. Make sure that you're not putting any unwanted stresses on the crankcase when mounting this way.

Hi!
Why?
Just mount the engines straight! Pointing them outward will not help much in an engine out situation!
On my DC-3 (Marutaka) I have zero down and side trust! Same on my Henschel Hs 129 (Dogfighter).