390 with c6 transmission

[dads1957ford]

Just bought a 390 with a c6 transmission  attached from a 67 mercury. I've read about the crossmember having to be modified to fit but just curious what I will need for a driveshaft. Will the original 57 work or should  I go back and get  the other one from the mercury? By the way, I have the shorter custom 300. Can't wait to get it on the road with this 390 setup. Thanks in advance for the help.