It depends on what you have in the wing now and what "spec" your bird was built to. Over the years the amount of washout has gone from almost 2" to .5". If it was me, I would be building with no more than .5" of washout if I could do it. You are limited to how much you MAY be able to take out by the way the ribs are glued in, the tank fastened in and if you have adjustment on each side. In the days of model airplanes we would twist the wing to put more or less in and hold it while we hit it with the heat gun to shrink the wrinkles in the covering. The covering would then hold it in place. I am going to attempt to take some of the washout from my Avid wing by making new struts from the rear lift struts from a PA-18 (streamlined tubing) and putting adjustment on both rear legs so I can crank out a bit of the twist. I can do it by hand and pull some out so I think I can get away with treating it pretty much like a model airplane and hitting the fabric wrinkles with the heat gun. If not, I will rebuild the wings and extend them and take out the 1.750" washout that is in it now.
If its an A model, someone cut the welded on mount off to put the VW on it. Your mount lugs might not be in the same spot on your fuse as the b and C mounts. Easy enough to fix it but something you might have in the back of your mind when your getting ready for the swap.
Boring day?? hahahaha and here come the folks to tell ya how great the overpriced engine is no matter what the costs. I do gotta agree with them. From the flight reports I have gotten, it is an engine that has yet to be rivaled. The Yamaha is probably going to surpass it with time, but IMO the flight times and flight reports are just getting going on the Yamaha and the data is not there like it is for the 912 series.
In your case, the prop is going to be what makes the difference. On Bob's KF IV with the 670 in it I can fly all day long at 3800 RPM doing 55 MPH. Will be interested to see how yours performs with that engine. What is the gear ratio?
I have had a hell of a time trying to find the original HH spar material. I would not have a problem using the kitfox spars (.063" tubing) and splicing on 18" and squaring the tips. Most of the forces are applied at the strut fitting and wing root and very little force at the tip. Adding length to the tips with wings that have too much washout in them anyway will really only add to the problem though in my eyes. If I was you I would just square off the tips and call it good on your bird or have someone do the glass work to fix what you have. Its pretty easy to shape foam and make a new tip or repair the one you have
I can get into your profile through the admin control panel but not when I click on it like normal. I have done just about everything I can think of to make this work. I am going to try and make a new profile for you, then merge the old profile with the new one and see if that keeps everything you have posted.
You might like your airplane better and have less trim issues if you run the CG back to around 16" or so. I highly doubt that language can get ya kicked off this site. I asked for a friend and he said that bad language was OK for the most part Just don't need ya posting pictures of the proper use of your device unless you have a pretty lady doing the modeling for ya!
As far as rudder trim goes, this is a pretty easy solution that could be done with minimal time and low material cost if one decided to fab it themselves.