need help with wilwood brakes!

I have a 72 dart that I'm in the process of converting over to bbp disc brakes. I want to order a set of Wildwood disc brakes. When I put the info in for a 72 dart it asks if it's a 9" or 10" spindle. When I put 73 dart in it asks if it's disc or drum spindles. Is there an easy way to find out what I have so I can order the right product? Any help is greatly appreciated!! Thanks in advance:)

P.s. if a pic is needed, I'll get one up after work tonight.