My friend recently replaced a ZF 5 speed and the clutch on a mid 90's F-250 that had a 300 six,I was amazed at the bulk of that thing,it looked like it belonged in an 18 wheeler,not a pickup !..
Only reason the transmission was replaced was it had 275,000 on it and the synchro's were dying from driving it too long with a clutch that refused to release fully..
Another guy I know has the same transmission in a 1990 F-450 Super Duty ramp truck..thing has never given any grief,but he did use a clutch up in it once in about 50,000 miles of towing..the clutch pedal bracket on that truck is cast aluminum,it actually broke in two,he had to get a OEM one from Ford,cost more than the clutch kit did too--was not fun to replace either!..