Hi there,
I got the yoke on the trans from the people I ordered the trans from. The key is to just count the number of splines, other than that they are rather universal. I then had my brother's truck parts business make me a drive shaft. It is not a big deal. Any reputable drive shaft place can make one for you. I don't know what rear you have but I have the 8.5 ford rear, which is very common. I don't know the part number but the guy who made my drive shaft was able to match it up quickly. The 8.8 rear is found in many Ford Explorers etc. It was a pain finding the correct bolt to mount the yoke to the flange. They are a Ford part. Some weird metric size. They cost about .80 each.
The drive shaft guy told me to take a measurement from the flange to the center of the hole in the yoke where the universal joint will be mounted. Ask the place who makes yours what they require. Also, before you take the measurement pull the yoke out of the trans about an inch to allow for travel. Keep in mind the car is going to weigh more once it is complete: Battery, full tank of gas, the body, driver and passenger. The more weight that is added the lower the back of the car will go and the more the trans yoke will enter the trans. I added weight to my frame before I took the measurement just to account for the items I mentioned. It may be overkill but you would not want to hit a big bump and not have enough play in your driveline. There may be an easier way to account for the weight, I just went with what I knew and what I had.
Let me know if you have any further questions. Sometimes expressing yourself in a text reply is difficult.
P.S. I just started my car this weekend. What a relief. There is a light at the end of the tunnel.
My Cobra page
http://www.jamswebdesign.com/cobra2/
Good Luck
Jim