Key word for this is “centershot”.
The majority of longbows are less centershot than the majority of recurves and the more centershot it is, the stiffer of shaft you can use.
That said, one needs to look at the individual bow’s centershot when choosing but even then it can become a trial and error thing and shafts need to be cut long at first and worked down. Well, NEED isnt the word………but should give you the best results tuning the shaft to the individual bow and also the individual shooter.
Not used to tuning with a 31 inch arrow but even then a 300 seems a bit much. I do also know that eastons recommendation chart CHANGED about 1970. IMHO I felt that was due TO more bows being centershot and the resulting change was stiffer shafts for the entire group.
LOTS will depend on the centershot and head weight but a little experimentation is fun and educational so give it a go and let us know how it works out.