This isn't a frame BUILDING issue, per se, but rather a question about frame modification.

I have two frames, a 1987 Schwinn High Sierra (yellow), which I ride just about everywhere, and a 1987 Schwinn Sierra (red). Both are 21" frames, are made of "4130 Chrome-Moly", and appear to have the same geometry. The main difference is that the High Sierra has a fillet-brazed head tube and triple butted main tubes, while the Sierra has a welded head tube and double butted main tubes. I do not know what the butting profiles are.
The Sierra frame is being built with a Staton Friction Drive gasoline motor to allow me to travel long distances at 25-30mph. I would like to carry a decent load front and rear (and in the main triangle or wherever else I can put bags), and I would like to address the frame stiffness issue I currently have with the High Sierra.
Last summer I did a self-supported trip on the High Sierra. I never weighed it, but I believe the bike and gear together were about 100lbs. The frame did not feel stiff enough for that load, and I could feel more movement in the front triangle as I pedaled than I would have liked to.
Another time while getting groceries I loaded my front panniers kind of heavy, with a moderate load in the Jandd Rear Rack Pack 2 on the back. I felt the same thing, with the main triangle flexing more than I would have liked it to. The load was much lighter, but I probably had more weight in my front panniers than I did on the trip.

So, without doing any welding or brazing to the Sierra frame, I would like to stiffen the main triangle to resist these loads better. I have access to a university's worth of machinery, and would like to machine aluminum clamps to add tubular 4130 members to the frame. I have a couple of ideas on how I might do this, but I'm not entirely sure which methods would have the desired result, hence my posting here.

Method 1 (Green): Add Mixte tubes from the head tube to the dropouts. They can be spread up to 3" apart at the head tube if need be
Method 2 (Yellow): Same as green, but bent and attaching to the seat tube lower down
Method 3 (Blue): Add what is essentially a continuation of the seat stays (like on a cantilever frame such as the Schwinn Heavi Duty), only the tubes are straight and not extensions of the seat stays. Probably spread about 3" wide or more to be out of the plane of the main triangle and to allow space for a frame bag
Method 4 (Orange): Add tubes alongside the top and down tubes to make it as if the top and down tubes were ovalized, the additional tubes being in contact with the original tubes

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(Black rectangles represent locations where clamps will be added)

Top tube is 28.6, and 23" long center to center.
Down tube is 31.8, 25" center to center

**I am also adding disc brakes to the back, hence the brackets (not yet finished) to brace the stays and strengthen the dropouts.
Ignore the 24" rear wheel. It's just in there because I was using the hub and qr to hold everything together, and it was nearby**

Part of the reason I am uncertain which method would work best is that I do not know exactly what the problem is. I know that the front triangle is deforming elastically, but I do not know whether it is bending, twisting, or a combination of the two.

If any of you framebuilders could chime in on which of these methods might (or might not) work, I would be very grateful.

I realize that I could find a stiffer frame and not have to do make any modifications, but I am committed to using this one.
I don't care too much about any added weight. I do care some, but not very much.
I am committed to only bolting things to the existing frame. I do not want to bond, braze, or weld.
This is the problem I am trying to solve, and the constraints I have given myself. It is as much an exercise for me in learning about post production modification and frame design as it is about getting the frame characteristics that I want.
Thank you in advance for any help.