I've put together a page on the internal workings of the X68000, and I think it's the single largest collection of information on the English speaking web.
http://nfg.2y.net/games/x68k
There are some comparison shots of X68000 Strider + Ghouls n Ghosts vs the Arcade (And Genesis) versions on the above page. Here's a couple of new galleries:
http://nfg.2y.net/games/x68k_Gallery/index.shtm
http://nfg.2y.net/games/x68k_Gallery/index2.shtm
[Edit] - Floppy Sleeve Art!
And of course some pinouts have been available for a very long time on GameSX.com (Which is currently flaky 'cause the hosting company is f**king useless).
As a bonus, there's a super GnG comparison page with X68000, Arcade, Genesis + SuperGrafx screenshots.
And last, but not least if you happen to own one of these, X68000 Power Supply Replacement details.
