Ahh, geez, oh how one can waste away the hours messing with Macs!
A Gossamer LB fits nicely in a IIcx box:
Slot-load combo drive from a TiBook. :d
several more pics:
How about a B 'n' W LB? A tad large, but could be made to fit:
I tried a Quicksilver LB but it's too big.