I've been going through the same thing myself, so I'll put in what I've learned so far. BTW, sparing details is not a bad thing - no superfluous info - but knowing what car you're talking about is not a bad idea.
I'm assuming a 74-89 narrow body.
As far as I am aware, there were only 2 993 front calipers, regular and the 'Big Reds'. They're not necessarily early or late, but big and bigger, the latter being for the 993 turbo and RS which used 330mm dia rotors vs. 322 for the regular 993. I can't help with the part #, and they are hard to tell apart if you don't have them side-by-side. I'll go out and get a measurment off mine later; the big reds are longer overall.
It's hard to see how much clearance you have from the photos, but if you've got more than a couple of mm's and the pads fit, I prob wouldn't stress. To center the calipers you'd need to mill the adapters or use different hats - much work/$.
There are 17" Fuchs style wheels available - do a search on 'Alton + wheels' or 'Rota Fox' (though I don't remember ever reading about brake clearance in conjunction with Rotas - maybe someone else can chime in here). There are also custom wheels - search Lindsey or True Design.
If you have the regular 993/S4 calipers and not the big reds, you can fit 16" wheels although you'd prob need different adapters and rotors. They fit using 930-sized rotors 304x32 front and 309x28 rear. Rears are best done with stock 930 rotors - not terribly expensive and work perfectly with the parking brake. Fronts can be done a couple of ways:
- stock, early 930 2-piece rotors - vfe, very expensive
- 993 2-piece rotors with custom hats - best method and OK budget-wise
- 993 1-piece rotor over slightly turned down 944 hubs (I still need to finish researching this - Steve Timmins/Instant-G has these available as 'custom hubs')
http://forums.pelicanparts.com/showthread.php?t=217751
I know what you mean by feeling humbled. Most of the above info is thanks to Bill V.