Thanks for the reply ....

"the clamshells drive is recessed about 2 cm from the outside of the case"

yeah hookem2oo7 that was my main concern - I haven't been able to map out where a combo drive would fit ...I think I may take a trip down to the local mac repair shop with my clamshell open and see if I could eyeball something that might work without getting too messy.
I was told the early gen. combos for the ibook would be recognized - but don't know that for certain either.