Low speed rattles?
There's a few common places that annoying rattles can resonate from on ye olde GS. One of them being the clutch.
It's a heavy unit to be spinning around on the big needle roller bearing and you will always see and feel the [normal] movement when you get hold of the clutch basket. Considering that the huge helical gear around the outside of it is being driven by the crank itself, movement isn't what you want. That sort of freeplay doesn't really matter, for instance, if the clutch is being driven by chain or belt as there is more flex. Gears don't exactly flex, but they will wear.
On top of this, there is a gear sat behind it, driven by the basket, which then drives the oil pump. A lot going on for something that only has one bearing.
Now a couple of the intelligent folks at GSResources forum removed some of the play by machining a little off the bearing hub that runs on the inside of the needle roller bearing. In effect, this removes a little of the end float and holds the basket at the angle it was designed to run. Thereby keeping the gears at the correct angle, and reducing some of the noise inside. Sounds good huh?