-only thing i would be scared of is if it gets really hot out and the bolt expands faster then the cast spindle does and your hole either elongates or cracks just like ice in a hole does.
(I don't know how to do the tricky thing with the quotes like you guys do)
You don't have to concern yourself with the temp outside. It's in the 250+ temps you should worry about (but still not a concern if properly "engineered".)
The proper way to do what is in question would be to use a bolt with a grip length (the unthreaded portion of the bolt) that extends through both parts. The tighter the tollerances the better, use self locking nuts and torque the bolt properly.
The place where I get my uni-balls is HM engineering at
www.hm-engineering.com
I don't think they sell to the public tho.
A 1" uni-ball is about $115 but is definately larger then anything you would need on a frame dragger.