What is the best route for a custom driveshaft build? It is for a street car. I need everything from front to rear. Do I try to accumulate the pieces and have it put together or let the driveshaft shop procur the parts and do it turnkey?
Or do I try to shop for a used driveshaft and have it shortened and balanced?

I've bought driveshafts at the u-pull-it that have the slip-spline and rear yoke for my trans/rear end yoke application, which is a 904 using 7260 u-joints. Then my local driveline business cuts off the ends and welds them into the appropriate mild steel tubing. Much better than the old, used & rusty original driveshaft tube. I finish it off with solid Spicer u-joints and a billet yoke in the rear.

But double-check with whoever will be doing the work to make sure they can get the correct diameter tubing in whatever thickness they recommend for your ends.

Make sure you find a GOOD, reputable shop and triple check the measuremenst, or have them check it before assembling the shaft.

I use these guys:
http://www.dennysdriveshaft.com/

I've already been through the used drive shaft bit. It ain't any fun replacing the tail shaft in the transmission, among several other things, chasing a vibration caused by the drive shaft. Denny's drive shaft has a customer here forever.

I used Dennys for two different NMRO Trucks in the mid 90's and great service. The "Stock" class was a 79 RC with a 440 and six pac pushing 575 HP and 650 Tq and had no failures. The "Mod" was a 77 F150 with a 503 (460) with 780 HP and a 250 spray, put a kink in the rear shaft and they replaced/fixed for free.