My opinion is do the conversion. With a series 2 3SGE it is not that hard at all. You already have all the bits of the 2s to do it. Just have to customise the engine and gear box mounts - and of course a few other smaller things. But you would probably come across such things doing any engine conversion.
The BEAMS 3SG is a bit harder to get in. Two piece sump and all that, and massive inlet manifold. But if your running carbs that will make things easier.