Sorry...that won't work properly, while yes it will fit, it provides NO support. The Pivot to "H" bracket has a 1MM clearance (varies on 85-87) and needs both upper & lower "H" bracket to engine mounts to be used and stabilize the engine while it’s running & frame flexing during sue. The bracket then will not tend to pivot or twist, as it is being properly supported top & bottom, and the engine centers itself as needed.I didn't say cut the frame! I said use the 86-87 rear engine mount that goes with the 86-87 swingarm & cut the top tabs off of it!
Now, I know you will likely say "I’ve done this before, I am sure you have, however; your suggestion is not sound nor is it correct....don't cut the top tabs of the 'H' bracket....get the correct frame.
Let’s do it correctly, or don't do it at all...!