Advice on rear main seal replacement

[slugish]

Have a 400 sbc with the good ole leaking 2 pc. rear main .Always leaked , just getting worse. Question , even though I know its best to remove engine for this , has anyone ever done it or know of anyone who has done it with the engine still in. Why in the world I didnt do it while the engine was out doing a head & cam upgrade is beyond me ,just not thinking . I really dont want to take engine out again if I can help it.