1983 GL 1100 handlebar grips

[billball]

Hi everyone,
I'm still learning about my 1983 GL 1100
I purchased this bike in awesome condition but the handle bar grips (foam rubber) are badly weathered and need to be replaced.
The left side end piece of the handle just un screwed and came off and the new grip puppies handle went right on with soap and water.
The throttle side just spins and spins, I already cut the factory foam grip off and there is no way the new grip is going to fit over the end cap so without removing the end cap
Any help from you guys would save what little hair I have left.

Thanks
Bill Ball
ps I just don't want to force it yet