I just bought an S12 with a VG30E in it, and i was wondering if the FJ20 from a DR30 would fit into it easily

Only if you have S12 manifolds and engine mounts . Hard to get but make me an offer .

I run a DR30 FJ20et in my S12
the left engine mount has to be remade to clear the turbo.the firewall need a small massage as not to be too close to the dump pipe. and a good idea is to sheild the fire wall with some thin alloy. The intake manifold can be shortened to clear the clutch master cylinder. Or if you can find either a N/A or turbo FJ S12 intake manifold like i did. If you can find a low type rocker cover off a S12 N/A FJ20 at the same time as the intake manifold as it won't hit the bonnet.
So with all that the engine fits snug.
Cheers
Brian