also do not shorten a driveshaft yourself, its asking for trouble
I have to agree with TylerZ281500, it's asking for trouble if you don't know what you're doing.
I've had a few customers come in the door looking for driveshaft work. That's coming in the door of a structural steel fab shop. Ive turned most away. Only do the ones that customers agree to the "should never be used" line on their invoice.
Not hard to shorten or lengthen a drive shaft but the problem we've had has been the balance. There are little weights on most of the ones I've seen. They are added when the drive shaft gets balanced. We can cut it and weld it and make it square and true but if you are out of balance we can't help you. I've heard of Vibration issues at speed. If it's a mud truck guys don't usually care. But a highway driver can be an issue.
Now some of the ones we've done, customers haven't had problems with. But it's hit or miss. If it was me, I'd try to do it myself and then bring it to a driveshaft shop to make sure it's balanced if I had problems. But if you don't have a lot of steel fab experience then it'll probably be cheaper to bring to a driveshaft shop than to spend your time getting everything perfect. Has to be tacked up perfectly square and straight and must be done in such a way so as it does not move during welding (from the heat). Also need a good solid weld on there. A lot of torque goes through that shaft. Not a job I'd do with a garage model gas-less flux core welder from princess auto or Canadian Tire or some similar pos. But if you have the right equipment and know-how, it's not that hard.
Edit:after re-reading my post, I just want to make clear that my opinion is a general opinion. I don't know what experience OP has, and I'm certainly not implying that the OP doesn't know what they are doing. For all I know the OP has been doing steel work longer than I have.