One of these will do for pushing a broach.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=33497
I used a similar one to make key ways. It does not take long to index the supports upward and resume broaching. Repeat until finished.
My friend Island may be able to help you out with pinning the bar in place. I don't know if a 1/4" dia. pin in shear will be sufficient?
A easy way to key a shaft is to drill and ream along the length of the shaft, on the seam of the mating parts for a pin. This arrangement places the entire length of the pin in shear. Think of it as a easy to make key way
