Sully said:
It's as easy as unbolting one, and throwing the other in. Only thing you may wind up playing around with, is some of the brake hardware if the 30 had drums. If it had disks, then it's about a half an hour project.
True....the D30 should have drums....but I think the D44 soft brake lines will bolt up to the hard lines.
You also may want to snag a 1978-1980 (its a disc/drum) MC for a SII and you will need a disc/drum ppv....if best I remember.
I've had tons of brake issues with my SII so I know you will have to have these IIRC.....unless you are converting the rear to discs too...then the drum/drum M/C and ppv you have already will work great with four wheel discs.
HTH