1951 Flathead to C4 drive shaft advice

[TJ]

You really need to talk with a competent driveline service company. These people specialize and they will tell you what you need in the way of a new driveline. Your old driveline will not work as the front yoke will obviously not fit the C-4. The existing tube may not be the correct diameter for the new front yoke and your tube may not be the correct length. Do it once and do it right.