J/29 Frac will have the same foot but the hoist will be almost 4 inches too long. If the sail has been re-cut previously, some of the hoist may have been eliminated so it will fit like a glove then. I have an old j/29 sail that I use.
A J/29MH won't fit at all (too short and the foot is much longer).
I wouldn't worry that it is underpowered. Most J/29 fracs have big roachy mains with a lot of power.
If you have one already, why don't you hoist it up and see if it fits? If not but it is in good shape it would be worth it to get it cut to fit.
