What Jug said.
The Mk1 Pre-facelift model was made up, I believe, of the SP1, SP2, SP3 and Lusso models. The Sport Pack ones came with side skirts, different sized and styled alloys, and better suspension. The SP range ALL came with uprated suspension but I think the numbers differentiated between what wheels came with the car, and possibly spoiler size/style etc.
Ideally I'm after an SP3 1998 V6 as it's pretty much the best (In my opinion) one you can get.
The later models had a Veloce badge which was the sport version of the old SP range, I believe this came with Recaro bucket seats made of grey cloth as opposed to the MOMO leather, they look GREAT though.
The Veloce could have bits and pieces added on to it though, different wheels, big spoiler etc.
But I'm not sure what the original Lusso and later modeled Lusso came with.
The 156 range still confuses the hell out of me though and I've probably got most of what I just said wrong,
Hopefully I havent though.