There are maximum lengths you can have a single drive shaft. The best is to consult a reputable driveshaft shop as for the maximum length you can go with your driveshaft at the rpm you expect to run at.
Less than 5 feet seems to be the magic number, or at least it was on my 1959 GMC longbed. I believe I am running a 4 inch tube. The shop that initially made my driveshaft didn't do a best job as I had a bad vibration at 3000 RPM. I ended up having that driveshaft made 3 times. The third time was because it dropped when the rebuilt rear end failed.
