No rubber spacer (vibration isolator) for the gt2a-s frame, engine mounts on the frame. You can put rubber, leather, or whatever material you want between the engine and the frame.
China engines come with a 1.25 in. diameter (.625 in. radius) front engine mount and the front frame down tube on the gt2a-s frame is 1.5 in. diameter. I'm a big believer in, "kiss" (keep it simple stupid) so I instead of buying or making some kind of mounting adaptor I simply bored out the front engine mount to 1.5 in. dia. it took me all of 15 min. to set up a mill and bore out the mount.
The gt2a frame has a welded engine mount on the front down tube, and no it does not come with a vibration isolator. I made mine from the handle of a grill brush that I bought from home depot for $3... Hope this helps