you can do it with the engine in... you would need to just remove the exhaust, thats about it.. well take the sump off of course,
BUT... if your big-ends are on their way.... just simply changing the wont help and you may open a big ole can of worms by doing this.. my advice be take the wole thing out, which is not a masive job really and get it done on the bench..
if your rings are ok ect and your main bearings are ok... you may do well to change the oil pump for a OE item whilst you are taking it apart..
goodluck

Lee.