I'm assuming that the springer was installed on that frame at some point in time...right..??
Just to be safe.. Is the stem of the springer 1" from top to bottom..??   it doesn't step out to a larger dfiameter at the bottom of the stem..??

The wheel... Measure the inside of the existing bearings in the wheel.
Then measure the hole that the axle slides through in the rockers.
They should both be the same size.. and I would think thats 5/8".
I can get you the axle you should need as well as wheel bearings if you need them..

Build it the way you want it ..... then learn how to ride it like you own it..
www.lowridersbysummers.com