I had the same issue adjusting the lower BS sprocket. I tried with adjustable wrenches and every thing was just to tight, awkward to get to, and I could never get enough torque on the bolt without moving the eccentric around and over-tightening the bs belt.
Once I bought the item below, it was really a matter of minutes and I had everything adjusted and torqued down to 35 ft lbs with this thin wrench.
Worth its weight in gold.
Special Tools for 944/968