Transfer Case ID

[dabarber]

I have a 1969 GMC K25 that I believe has a 400CI small block with a TH350 transmission. I know it isn't stock, the VIN says it came with a 305 V6 with a manual 4 speed on the floor. I am trying to figure out how to shift the transfer case. It just has one lever (the Hurst). This lever shifts from H to N to L, I think. I can crawl underneath and move the other lever manually and it takes it out of 4WD and the other way (it only has two positions) is 2WD. There is no tag to tell what transfer case I have, but I think it is a NP205. According to the numbers on the front of the block, the engine came from a 1978 Chevy 4X4, so I'm assuming the transfer case came from the same. Can someone tell me for sure which transfer case it is and what's up with the single lever shifter?