Depending on your state, you will either use level 9 rules (there may be some minor modifications) or NHSF (National High School Federation) rules. If it's NHSF rules, I would inquire about whether it's allowed. Last year was the first year yurchenkos were allowed due to safety reasons. FHS onto the board is not a vault listed in the NHSF code of points so it may still be discouraged (or it may be so rare that it just wasn't added to the rules). A yurchenko vault has the same start value as the same non-yurchenko entry vault, so a FHS onto the board, FHS onto the horse would likely be worth the same as a handspring vault (8.6) if it were allowed.