6900 and 6901. Just for fun a couple you tube videos.
The 6900 is quite mild and the 6901 is a bit angry at idle. Interesting the @.050 specs are a bit different but the advertised specs and lift are similar. Listen to the videos. Of course the timing and carb adjustments are different.
#6900 1200-5000 rpm
204/214 278/288
421/444 112°
#6901 1800-5500 rpm
218/228 276/288
441/441 114°
#6900 video. Idle at 2.00 min.
#6901 video sounds like it's hangry and needs a Snickers!