Someone with an SE/30 will have to verify what I say here, but as the owner of many different kinds of Compacts, including a Plus, I can basically say for certain that the only differences between any of them are slight cosmetic differences on the casing and the capabilities of the various components.
So you should have no problem with your transplant. Just keep in mind that the Plus was not meant to support an internal hard drive, so if you want that SE/30's hard drive in there in addition to the floppy drive, you'll have to get a bit creative. I believe there's a special bracket that a third party company sells to aid in this.
Compacts: Macintosh SE, Macintosh SE, Macintosh 512k, Macintosh Plus
Other Macintoshes/Apples: Macintosh Centris 610, Macintosh Quadra 660av, iMac G3 Indigo, Apple IIc
Non-Macintosh: Soyo PC, HP laptop, Atari 800XL, Commodore Vic 20