SEL69L, you say that you have seen pics of this installation in American cars - do you have further details on that, or where I could find those pics ?
Mark, there are three bolts that are the same size as the original ones that secure the steering box to the chassis member. The additional three bolts are drilled through the chassis member and are then secured on the inside (next to the steering box) by three lock nuts. Thus, once this plate is fitted, there are then six internal sleeves that hold the two assemblies without the likelihood of the chassis member being squashed or distorted. I mean, it's got to be an improvement and provide additional strengths.
Just a word on gusseting, plates, additional tubing, quality of steel etc. Many years ago, I went to the vintage bike races at Amaroo Park and met up with the importer of Montesa Motorcycles at the time. In those days, I had a Montesa 1974VR fitted with a non-standard 360 engine. Anyway, in the races that the two Montys competed, one was always in front, or close by, whereas the other kept onlanguishing mid field. Remember, two identical bikes, both 250cc, why the difference in speed etc. So I asked the guy, and he explained that one bike was running a normal steel frame, whereas the other had a chrome molybdenum steel frame, adding greater strength and stiffness, thereby the bike handled so much better ! I thought that was interesting. Nowadays, quite often you find stiffening struts under the bonnets of high performance sports cars, and those struts run from one side of the car across to the other side. In addition, many times, when a new car, or chassis are evaluated in tests or advertising blurbs, reference is made to increased stiffness of the body providing better handling. Thus I consider that this plate would certainly provide rigidity in an area that is under considerable stress at all times, considering the weight of engine and weight of the body. Just my opinion. Regards Styria