Clutches in a powerglide are huge, there's plenty there to stand up the heaviest car. Here's a scenario for you, so you think T350 clutchs are small, look at the inards of a ford C4 and you'll think that the T350's are huge in comparison, But that little C4 has stood up many a stang on the rear bumper and propelled them into the sub 7's in the 1/4.
I had a friend that built up a 501 caddilac motor and put in in a mid eighties cutlas, welded up the spider gears in the inheritly weak 7.5 to make a red neck posi and get this, put a bone stock 250 r over drive tranny behind that torque monster, ran low sevens in the 1/8 and never missed a beat in the three years of that I knew he had the car. So it goes to show size doesnt really matter in a tranny as far as the clutches are concerned anyway, most times its the other things that fail like planetaries, sprags etc.
JMO
><Cp