I'm baffled, but here's my best guess:

C230 Kompressor = supercharged 1.8? or is it 2.3?
C230 (no Kompressor badge) = Still supercharged or not?
C240 = ???
C280 = 2.8 liter V6 n/a?
C320 = 3.2 liter V6
C350 = 3.5 liter V6
C32 = 3.2 supercharged! (100% sure)
C55 = 5.5 V8.

Got this on Wikipedia:

C-Class Displ. Power SCoupé Sedan T-Model
C 160 1.8 L 122 PS X
C 180 K 1.8 L 143 PS X X X
C 200 K 1.8 L 163 PS X X X
C 230 2.5 L 204 PS X X X
C 280 3.0 L 231 PS X X
C 280 4MATIC 3.0 L 231 PS X X
C 350 3.5 L 272 PS X X X
C 350 4MATIC 3.5 L 272 PS X X
C 55 AMG 5.5 L 367 PS X X
C 200 CDI 2.2 L 121 PS X X X
C 220 CDI 2.2 L 150 PS X X X
C 320 CDI 3.0 L 224 PS X X

C230 Kompressor = either a 2.3k or 1.8k 4cyl depending on year
C230 (no Kompressor badge) = 6 cyl non k 2.3(not sure about displacement)
C240 = 2.6 n/a 6cyl
C280 = 3.0 liter V6 n/a
C320 = 3.2 liter V6 n/a
C350 = 3.5 liter V6 n/a
C32 = 3.2 supercharged! (100% sure)
C55 = 5.4 V8

C230 Kompressor = either a 2.3k or 1.8k 4cyl depending on year
C230 (no Kompressor badge) = 6 cyl non k 2.3(2496-cc DOHC 24-valve 90" V6, N/A)
C240 = 2.6 n/a 6cyl
C280 = 3.0 liter V6 n/a
C320 = 3.2 liter V6 n/a
C350 = 3.5 liter V6 n/a(=3498-cc DOHC V6)
C32 = 3.2 supercharged! (100% sure)Woo Hoo!
C55 = 5.4 V8(=5439-cc SOHC V8)

MBZ kind of gave of on the nomenclature matching the displacement several years ago. Now, the C230 means it is their entry level model, even though it has been upgraded to the 2.5 Liter V6. Use the numbering system as a sort of "caste" system for cars.

So then at one point in time were there really four (or five) V6 engines available, or was there no overlap on some?

I see a 2.5, 2.6, 3.0, 3.2 and a 3.2SC. Were the 2.5 and 2.6 available at the same time? Also, the offering of a 230 V6 and a 230 I4 seems "unfair" to the V6 buyer!