1969 cutlass engine swap
 

I just bought a 1969 cutlass with no drivetrain and no driveshaft. I'm dropping a 455 that came out of an 1976 ninety-eight as well as the th-400 trans. A friend gave me a driveshaft that fit both the trans yoke and the u-joint straps,but its too long. Is it well recomended to have it cut at the ends and welded or just get a custom one

I would never cut a drive shift and weld it. It would just be a matter of time before it breaks. There are lots of places that do custom job.

You can have a shop shorten it. They will remove one end, cut off the extra material, re-attach the end, balance it and give it back to you.
I would price having that done and the price of a new one. It might be worth while to just get a new one.