The only axles that fit in a Mustang II 8" rear end are custom made ones or stock Mustang II axles! Some say maverick (Too short), Some say 60's Mustang(too long). I beat the snot out of the II all summer 300HP + 100HP shot of nitrous. Have your axles re-drilled or have some new ones made. In your case the re-drilled Mustang II axles will be plenty strong enough.
http://forums.stangnet.com/738531-or...new-axles.html