check out CPP for conversion axles for the 63-69 55.5" axles, here is the info that I have for the axle set
conversion axle set 67-68
part number 6369rac-5
price $289
website link
http://www.classicperform.com/Store/.../6369RAC-5.htm
thats the axle set that I have purchased for my build. I am currently in Afghanistan, so I have not had the opportunity to verify the fit.
had some long talks with customer service about the axles, and he assured me that they would work.
keep us informed