On my 360 in my 74 swinger I will be running a built 727 that is supposed to hold upto 650 HP and currently have a 727 behind it now and it puts out around 400 HP
My dad uses a 727 on his big block 68 charger for 20 years no probs with 450 hp going through it
And he has a buddy that has a 900 HP big block dragcar with a built 727 and had a built 904 behind it before that grenaded mid way through a pass