You can't get the Countershaft Center closer to the Swingarm Pivot Center?
A 'rough' C to C nowadays is around the 70 / 60mm (or less) C to C on bikes with LTR. Your positioning looks Hugely longer.
Look to the original CC to SA distance and Height to have the rear suspension work as it is intended. The Original Distance And Height of the Center to Center is what the Suspension / Chassis was designed for.
I understand that the Diameter of so many Motors presents difficulties, but that distance shown was the sort of thing that created So Many Problems (thrown chains, dreadful effects on Suspension action, Rapid Swingarm protector wear and Swingarms sawn through by the chain etc) in the 70s during the suspension revolution.
Believe me, I was heavily involved with said "Suspension Revolution", and we largely learned the (at times, Very) hard way.
At the minimum, you'll have to try the sort of lash ups that were done in those time periods - springed / pivoting chain tensioners.
A Jackshaft is the sort of thing that can help with retaining an original CC to SA distance if you can't move the Motor closer to the SA pivot, but, they of course have their own set of problems.
I'm Not slagging you, just trying to help you.
