At the risk of sounding like a fool, are the ikara props easily attached to the Ray Harlan assembly? And, if so, is there enough of a difference that it is worth it?
Are you comparing this:
(is this what is considered the Ikara prop hanger)?
and the Ray Harlan assembly?
If that is the ikara prop hanger then: when i did WS i used the freedom flights kits which used the ikara prop hanger which worked fine. The prop fits well into the hanger. the hanger is glued fairly well into the Motor Stick, you just have to make a cut which a part of the hanger fits into. I dont know if it's much better using the ray harlan assembly. I dont see any benefit except for less weight, but for WS the weight limit is easy to get close to.
Also thinking about Jeff's comment, the ikara prop hanger makes the prop detachable.
For the Harlan SO thrust bearing you can use .020" music wire for the prop shaft
for the Harlan Penny plane the hole is SMALLER, so you need less than ~ .017" MS