I can't imagine that corrosion would be such a problem, you would want to encase the rods in tubing.

If they do get corroded, it may be time to change them out anyway.

IMHO a better solution is to assemble the rods, get them to the right lengths, fly the plane to make sure the trims are right, then remove the rods and dip them in polyurethane and let dry for a couple of days.

The Poly will leave a thin transparent coating behind.

Re: Engine.

You normally remove / fix this before fiberglassing....

The DLE is going to produce more torque and vibration than a 2 or 4 stroker.
I wouldn't reduce the beam thickness by grinding some material out... better to get a larger beam more suitable for that engine...