Shimano rear cassette on cruiser?

Hello all. I got a couple of running bikes, and I intend to build (gasbike) one and use the other for parts.

I would like to know if anyone has experience with putting a rear cassette and derailer on a Del Mar Cruiser? I have no idea if this is even possible. It seems that I would simply gain two pedal speeds- is this correct? If so, would I benifit from a smaller pedal crank? I assume I will need a longer axle?

And finally, can anyone recommend a place where I can look at exploded diagrams of rear motorized bicycle wheel set-ups? I don't even know what should, and should not be between my chainstays!

1) The donor
2) The donor shifter
3) Pedal side- my current rear hub set-up. Works- but it ain't right. It is a motorbicycles.com heavy duty rear wheel kit.

A million thanks for any help.

That's good news- thanks!

So I'll have 3 pedal speeds, any thoughts on a smaller crank?

I'm not sure what it's called, but the part of my hub that the (again unsure- rear gear, the pedal chain goes to it, not a brake) threads onto, isn't wide enough now, let alone with this cassette. You can see in the 3rd pic.

Any ideas?

I'm considering building a new rear wheel... bulletproof as I can. Time doesn't allow for ordering parts quite yet. I'm going to have to make due with what I've got on hand.