Apparently there is a benefit to be gained from having a HiFlow head on an older engine. Sommer do what they call the "red head" flow job on older heads which, they claim, takes the head to better than a stock HiFlow. Also their advice on airbox mods varies for the HiFlow - Older bike = airbox door but leave the snorkle in, whereas HiFlow = airbox door and remove snorkle.
Don't know if a stock HiFlow will bolt on to an older engine but I guess it should - shouldn't it?
A good friend will come and bail you out of jail...but a true friend will be sitting next to you saying........."Damn..We F*cked Up" - Anon.