Yes, your tank is absolutely a Heinrich. I had an identical tank on my own 1974 R90/6. I lived with that bike for decades, and can share some tips. First off, the rear tank mounting bracket has some adjustments. Make sure to use that and lift the tank up as much as you can. It that’s still not enough, use additional rubber washers on the base of the long bolt that goes through the tank into the toolbox area. I used gas tank rubbers from 1955-69 twins because they were about a 1/4” thick, but you might be able to source something locally. I didn’t like the look of the tank compressing the seat either, and was able to fine-tune that with the above process. jl