This is the bird cage approach made with a whole bunch of 1/2 
diameter .049 wall tubes. It is less complicated than  it looks.
Make a 1/4 scale balsa model to prove to yourself that it
will be rigid.

The rubber bushings are on the engine/psru/prop/
alternator/starter CG so the rear mount is trivial.
Little to no load back there.

The red tubes are the motor mount tubes proper. The green tubes
are necessary to insure the integrity of the RV4 landing gear.
If the transverse green tubes is not installed the landing gear will
tend to spread the motor mount tubes. The fore and aft green
tubes feed the landing gear loads into the motor mount.

The new tandem RV's are much simpler with a bent aluminum gear.
A lot of this stuff would be unnecessary.

A custom oil pan must be made to fit inside the bird cage.

When you use a pointy cowl like this kind motor mount implies
The mufflers are a problem. Perhaps Mike Wills twin
side mufflers will work fine. Lets keep our fingers
crossed. Here is a picture of Mike's mufflers.

Looks like Mike's engine is a bit further forward than shown
on this sketch. His rubber mounts are aft of the engine/psru/prop/
alternator/starter CG. This picture should also help you to visualize
this motor mount design.
 
Paul Lamar
 
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