True. Gearing is the same for all. The number of clutches (and therefore power-holding capacity) changes depending on application. The HD and V8s had the most, and weaker engines had less. For example, a Pinto with a 2.3L 4-cylinder and C4 will only have 2 forward clutch plates, as they found 3 or 4 to engage too harshly even with flow restrictors (and why Pinto valve bodies are specifically 'different').
I6 C4s can be upgraded with swap-in drums or by modifying the I6 drums for more clutches - but with all the C4 cores out there on the local Craigslist for under $50, why bother? On the other hand, if it's in nice shape, you may want to grab it if cheap or free just for the extra parts towards your next build. Lots of little stuff to use for HP building, like extra pressure plates, planetaries, shift lever to mod and stuff. I finally dumped a bunch of parts cores that were picked-over for builds just to make space. BTDT.
David