Combines vibration on steering column

I think your vibration is still comming from the sickle drive. I would replace all the bearings and be sure the sickle head drive is tight. It doesn't take much slack to cause vibration. With the cab door open and the header on, is there a "clicking" soundIJ If so, you have slack in the drive. When everything is up to "snuff" she'll be quiet.

does it stop when the header i son the ground solidIJ IF so it is the stabilizer. IF not do you have the variable speed locked outIJ

Might want to check shaft on rear of header where sprocket and pulley hub is.Had vibes in a 400 head there ,was a chunk out of the shaft.

I agree with tbran. Check the stabiliser. If the rod end breaks on the stabiliser under the feather sheets on the lH end of the header, the steering wheel will get a quite a shake up from side to side. The sickle guards can also be seen to get a bad shake up from side to side. Some vibration can also be caused when the stabiliser pivot bushes and the pivot shaft become badly worn which allows the stabiliser and the sickle bar to also develop a shake from side to side. Prompt fixing of this problem is essential as the parallel links under the feather sheets then carry the side loads and will quickly destroy the bushes in these links making for a loose and hard to adjust flex sickle bar. It is standard practice in our area to replace the standard mild steel pivot shaft with a chrome steel shaft made from hydraulic ram shaft steel. Doing this gives years of service from the stabiliser pivot and bushes rather than the usual twice a season replacement of the shaft and bushes that we had before this mod.