New guy needs help, chain problem

[JVROOM]

Motorizing an old schwinn beach cruiser. I used to consider myself a good mechanic. Can't seem to get a true rear wheel, 26x2.125 coaster. Tried one from Huffy, sta tru from Amazon, one from a local bike shop, all way out of alignment, wobble, wobble. Took one to a bike shop, they said forget it, tried truly one myself no luck. Thinking about worksbikes rim, or going to something narrower?
Second problem is the chain keeps derailing on the rear, wiped out two chains, a coaster brake arm, a rim, drive gear and the chain tensioner. I've tried three different chain adjusters, a couple of those spring loaded ones, no good. I flipped the drive gear over so the teeth were closer to the outside which helped with the chain is still running to the outside edge and jumping off. As you know it's kind of a pain to unbolt that gear and bolted back on but it almost looks like it needs a spacer and a half?? I hope someone could help me thank you for your consideration

 

[JVROOM]

Here's an update, I found out that chrome rims for these types of bicycles are not true, it has to do with the way their manufactured. They can be true to some but they're not going to be perfect like an alloy rim, some wobble is going to be there.

I also figured out, that by the time you tighten down the rear drive gear where it starts to compress onto the coaster brake Center it so tight you can't get it lined up perfectly and is therefore out of round. I suspect that higher speeds and jacks the chain back and forth causing problems.

I found a clamp axle mount drive assembly doesn't use those rubber fiber gaskets from piston bikes, maniac part, waiting for it looks promising, still would like to hear from anyone has any thoughts thank you, John