just to get it to run, jump a positive lead from the battery to the input side of the ballast. then bridge the starter relay and it should turn over and try to fire.
It should run like that just fine.

BUT in 73 I think you have an interlock in the column where you can't put it in gear till the key is turned. you will have to defeat that if you want to shift gears.
Then it might be easier to find the instructions on popping out the switch.
then you can start it without the key at all.