Yes I am an EE, and I know what it takes to compare those two datasheets *). I just question your notion about "it does not take a genius to work it out", as you obviously didn't get my comment about the elctrical, timing, and functional comparing of each pair of corresponding pins of 3430 and 3630. It's not sufficient when they share the same signal name. And even this very low level simple signal name comparing can't be done in a proper way in that little time it took you to come up with your bold statement. I'm used to doing things like these (it's actually my job), and I could at very best give a first guestimate of "looks like they follow same pinout scheme, on a first glance", after 30 minutes or less.

And no, I'm not going to do this fancy of checking every single pin pair, just to come up, ideally, with something like "pinout, timing, electrical, and function - all drop in compatible. Buy a TI Zoom (USD2500), unsolder the 3630 there, and replace the N900 3530 by that chip. Expected yield (when done by really SMT experienced EE): 10%, so better get 10 Zoom and 10 N900, to end with one working slightly pimped n900"

Sidenote:
If gta04 project of goldelico would've seen ANY chance to get 3630, you bet they would have picked that processor.

*) I even got the several "datasheets" of OMAP3430 on my PC here, each of them >>3000 pages. CBA to find and dl the 3630 datasheet megabytes, just out of curiosity: You found a link to them and got them, abill_uk?
/j