Question on 1966 Mustang 3 speed transmission

Hi - a friend of mine is looking at buying a 1966 289 V8 Mustang
with the 3 speed

Someone is telling him these are not very strong transmissions and to
avoid the car - I thought V8 mustangs used the same unit as most of
the other small block fords and that this tranny is pretty strong

I'm not sure if someone is thinking of the English ford transmission
that they used with some of the early 6 cylinder cars ( and I think I
read somewhere that unit was a 4 speed) which I understand was not a
strong tranny

Anyway if someone could clarify on this point that would be
appreciated - it is a nice car and it would be too bad for him to miss
out on it because of some bad advice

Thanks