I take it your doing a 1 ton tie rod setup with Chevy tie rods. The reamer you need is a 1.5"/ft taper also known as a #2 ball joint taper they have a size range of 7/16-1".
The right hand 7/8-18 tap is easy to find there are very few places that carry the 7/8-18 left hand tap. The cheapest I found is from McMaster-Carr at $91 each I figured threaded bungs were cheaper.
Left handed 7/8-18 tap http://www.mcmaster.com/#2584a917/=3hgefb
Ace Hardware where i work has it. i was suprised we had it. it was a special order for a customer who decided in the end he didn't want it so we put it out on the shelf. :lecture: