Classic/Antique Car Repair: 65 mustang top loader 4 speed tranny, speed tranny, shift fork

Question
have lost 3rd & 4th gear still have 1st,2nd and rev.
i was speed shifting. there is no noise coming from tranny and it fell as if the gear shift is engaging yet no 3rd or 4th gear

Answer
Since 3rd and 4th gears are operated by the same internal shift fork and the same synchronizer drum it is one of the two. The shift fork could have broken or the gears could have been stripped on the synchronizer drum. If the linkage is moving on the outside of the gear box, then it is time to remove the transmission for work.
Brad