An A600 laptop looks relatively simple, if the right parts are obtained. Definately want to try and use the same screen method Ben Heckendorn uses for his Atari laptops.
You could remove the 23 pin connector entirely, and wire directly to the holes. Ditch the RF adapter, and replace it with an S-Video connector with a Neobitz (mine just shipped today... I'll assemble and test it, and post my results soon) if I find it works. Thus display AND video output would be awesome.
Definately yank the RCA connectors for the sound, and replace with a stereo mini jack.
Yank the power plug, and replace it with an internal 12V input power supply... Thus utilizing 12V battery power as well as a 12V external power supply, instead of that bulky Commodore one.
The mouse would take a little doing, but I'm sure something could be hacked. A PS/2 trackpad uncased adapted via a Cocolino adapter hard wired.
The rest of the board is already layed out in excellent design for a custom case. Original keyboard would work well. Even takes 2.5" hard drives. Plenty of slimline CDROM drives out now, Mini-ITX spec et, al.
My only question is, can an A600 boot from the external floppy drive? If so, you could leave the internal one out of the design, and get one made for a CD32 or something.
Honestly, the hardest part of any of this is the casework.