Ok, in response to PM's, here's how I do this.
First, the concept. My track (above) can easily handle C-can power. So then I thought, just put some mild arms in an old open setup to really get a nice tiny motor that is still manageable in a small / home track environment. I had a couple of G12 arms that fit some old open setups that I had, but these are just a bit too much for my track. That's when I had JH wind something milder that would still work.
First, I start with old, open cans / setups that are originally designed for .480 diameter arms. Now this is just a fun motor - no racing - so there is no reason to go over the top on costs.
I use Alpha bent metal cans and old plastic endbells. These are not listed on their website but I emailed them and they responded that they still have them in their vintage inventory.
Next, I use magnets from DMW Products. They have two sizes and I use the thinnest ones - .070 thick. Your can ID is like .635 so after you glue your magnets in you are left with a .495 hole - perfect for a .480 arm but not enough for my .495 special arm. I then hone this out to .510. Bigger arm + less magnet = less punchiness / more driveability. I'm sure these are not the final word in magnets but they are singles and cheap at $14.00 a pair (Forget about all that Koford and Camen stuff at $50.00 per pair).
Bearings: I just use a standard 5mm ball bearing in the endbell. For the can, however, I use a flangeless bearing so I can solder it flush to the inside of the can for maximum arm clearance. These are not standard slot car bearings. I think I get them at VXB.
The arm is a .950 in length and is a squeeze in this setup but I was very specific with all the dimensions to John. Everything just fits and I wound up with the motor above.