Can I replace my 383 rear main seal with motor still in the car?

So my motor started pouring oil today. Appears to be coming from the rear main seal. Constant flow of oil coming from rear of motor pouring down on the trans. Motor is a 69 383 and it's in a 69 valiant post car. Has anyone successfully replaced this with the motor in the car? And what seals are you guys having the best luck with?