That's what Im using I just filled in the gap between the end of the ergon grips and the brake lever mounting band

1st with a left over bit of cushion handlebar tape, then I just cut down a short section of a round grip and slid it on the bar
then fitted the Ergon grips back on.


IDK about the S-A 8 speed I stayed with the BSR (+ Mountain drive crank.)

Making a cross bar between the M bar's U uprights of more 7/8" tube ,
could give you more space to mount that grip shifter in the Center.
got any DIY fabricating creativity?