Most motror sprocks will not accept the 1/8" chain- I bought a narrow one a couple years back with the chain, and wanted to put it on a road bike- mostly to save weight.
it jumped the sprocket on first use- although it looked straight and I'm an experienced bike mechanic- I scrapped both it and the road frame because the clearances were a problem- and put it on a cruiser with 700c wheels. The 415 is a little heavy, but really does seem to have a "slop" factor on most sprockets- greater room for error. While I thought I could probably get it to work- I didn't want to be messing around with it- As it was, I lost the woodruff key in the mess, and had to get another one of those- so that little bit of metal cost me weeks waiting.
a 1.75 tire with a smooth tread will give you more clearance and have a better roll and a lot less vibration at motor speeds. Much lighter too. You can also get 1.50 or even 1.25. I've ridden 1.75 and they're durable, but I'd get 1.5 if I was buying 26" tires now- to me it's mostly about the roll.
If it's a freewheel hub- you can always get a little side direction with axle washers and spacers- Never built a coaster brake build, so I don't know there.
