6 volt horn in 12 volt vehicle

[oldforder]

I don't know if this questions belongs here or in the newer fords, but here goes. I have a 1928 Ames horn that was on my dads 28 Tudor that is all of it that is left. I would like to mount it on my 65 mustang. What kind of resistor do I need to make it sound right? I know it works on 12 volts but it runs so fast that it doesn't sound right. I want a cheap resistor, so was wondering if an ignition coil resistor would work, as it will not be used but for a couple seconds at a time.