Correct, the finger stop is just a keymod mount. There was one more slot forward, but I didn't feel right asking them to move it if I wasn't ready to make the purchase right then.
As for the extended stop, I've got a couple bars of 6061 left over from an old project and could always mill something up, but have never been a fan of anything sticking out past the end of the handguard (other than barrel/supressor) - even having my surefire sticking out an inch past the rail bugs me a little...
The shop I was in had 5 of the K models in stock, and mentioned that while the only difference was the barrel and tube/handguard, there was no intel on when (or if) Sig would be selling the barrel/tube parts individually.
If I had a timeline/expected pricing on those it would almost be a no-brainer, particularly as the K model was about $150 cheaper...