78T/a

I came here because I realize these are the transmissions you guys are mostly dealing with so i figured the good knowledge would be here. Im considering putting a 700r4 behind my 474 Pontiac in my 78 Trans Am. Im tired of driving around with a 3 speed transmission. From what I have read, these transmission dont do well with torque and my 474 packs a lot of it. Is there anyone running these transmissions and having then last in vehicles past the 600ft-lb mark. I looked at the 4l80 but im not sure Im willing to spend close to 4000 just for an overdrive

Thanks
Mike