R reg freelander - need new engine 2.0 l series

Hi to all. Im looking for a replacement lump for my 98 freelander. the engine im told is the same as rover 220,420 and 620 diesel's. I understand there are a few variations on the engine code such as 17n 20n etc can anyone help as i have three rover 420 engines that look the same but have different latter sections to the code? Its the 4 glow plug type if that helps. I have a fair understanding and i have already completed a head change etc on a friends l series engine so im going to brave it and do the change myself...... any feedback will be welcomed and yes i should of got something else instead of a freebie haha