"...The 45-70 case will almost for sure hang-up on the lip of the mortice. I've made a spring & plunder assembly to lift the block flush after initial extraction, but only for complete custom jobs. As said, the case is big enough to get your fingers on, a bit large for the action maybe, but they are plenty strong.
I suspect that would be the larger action??..."
I had a chance to talk to the folks at Dakota about the position of the block when the action is open. As I understand it, the block needs to drop down further for larger case heads, in order for the extractor to have room to swing through its arc. Which could be why the block didn't seem so low on a another rifle chambered for a smaller round (257 Roberts).
I'll shoot it for the first time this weekend and see how it goes.
Re the action size, I would guess this is the larger action. The options page from Dakota's catalog says the 45-70 is in the larger action. I measured mine, and it is 1.567" in width, and 2.420" in height, from the bottom flat to the top of the receiver's arc, but excluding the scope mounting block. Length is 2.079".