One other thought about all of this is that you're unlikely to get to 40MHz, but PowerBooks with '040s in them do exist if space considerations are above all else.
A day long first impression and a rant about a first time experience with an unfamiliar case design does not a final case make. I'll bet he'd have the same reaction to an 8100 after working on that pestiferous case the first day.
This gets back to an overarching point I've been making for a few years that Ll Macs are bad computers and most, if not all, of them have their own problems when it comes to really using them.
That said, the 630/6200 are put together in a way other home computers generally aren't. (Interestingly: backplane designs are very common in like UNIX workstations from the '80s and '90s.) If you see one and try to clean it out and you discover you don't like the design, I don't know if there's an awful lot to be done to change that, other than, I suppose, just not pulling it apart that way.
NoPro, apparently nobody can understand my descriptions. :-/
This is probably because I've never really taken the plastic cladding off a 6200 or 6500 but is what you're describing basically making the machine taller and less deep?
Because, IDK, in a lot of ways that sounds like a Quadra 650 to me. (THough: a 650 is still most of the depth of the 630.)
Regarding the a/v system: It was input only. There was a composite output kit that, if I remember correctly, tied into the video output modules that either connected the machine to the multiscan 14 built into the case of the 5200 or to the graphics output port, but I'd have to go look.
There are probably various revisions, but I don't think that they fundamentally change anything. I know for example there was a tv/fm version of the tuner, which would be better to have today if you had an interest in FM input.
You could also get one of the atsc/ntsc converter boxes and it should be good for devices (VCRs, et al) that could output to cable channel 3/4.