Buying a new gearbox

[Graeme76]

I am looking for some advice. I need a new gearbox for my 2003 LDV Convoy which has the 2.5 ltr Transit engine. The number on my current box is YC1R7003HG. Looking online there are a few available. Am I correct in thinking that as long as the gearbox code is the same the new one will fit? I have also noticed some are 3 flange and others 4 flange how do I check which mine is? Can the flanges be changed from the old box if I get the wrong one? Many thanks in advance.