Replacing Front Seal on a 727

If it were just me I'd just pull the trans. No need pulling the engine too IMO. No special tools required. They make a fancy seal puller but a large flat tip screwdriver inserted at an angle will work just fine. It's always possible you'll find the front pump bushing and possibly even the torque converter snout in bad shape on a 45 year old car. Those can be remedied easy. YouTube is full of video's showing work done on 727's. If I were you I'd scan through them and find the ones that are most pertinent and watch them.

BTW: Louis's tip on refreshing the whole trans. is not a bad idea especially if it's original because most likely all the seals are hard as a rock. There's a whole series of rebuild video's on YouTube from start to finish